Endless track for traction of a vehicle

ABSTRACT

An endless track for traction of an off-road vehicle, such as an agricultural vehicle, an industrial vehicle (e.g., a construction vehicle) or a military vehicle, is provided. The endless track comprises an elastomeric belt-shaped body comprising an inner surface for facing wheels of the vehicle and a ground-engaging outer surface for engaging the ground. The endless track also comprises a plurality of elastomeric lugs, such as drive/guide lugs projecting from the inner surface and/or traction lugs projecting from the ground-engaging outer surface. An elastomeric lug may have a material composition defining an arrangement of zones of different materials which comprises a plurality of zones of different elastomeric materials. The elastomeric lug may exhibit a desired variation of a material property (e.g., a modulus of elasticity) across the arrangement of zones of different materials. A zone of the elastomeric lug may have a dedicated function, such as a sacrificial zone or a wear indicator zone. An elastomeric drive lug may comprise an uneven drive surface, such as an angled or curved surface, for engaging a drive member of a drive wheel of the vehicle.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/325,783, filed on Dec. 14, 2011; which claims the benefit of 35 USC119(e) of U.S. Provisional Patent Application No. 61/422,968, filed onDec. 14, 2010. Each application is hereby incorporated by referenceherein.

FIELD OF THE INVENTION

The invention relates to endless tracks for providing traction tooff-road vehicles and to components of such tracks.

BACKGROUND

Certain off-road vehicles, such as agricultural vehicles (e.g.,harvesters, combines, tractors, etc.), industrial vehicles such asconstruction vehicles (e.g., loaders, bulldozers, excavators, etc.) andforestry vehicles (e.g., feller-bunchers, tree chippers, knuckleboomloaders, etc.), and military vehicles (e.g., combat engineering vehicles(CEVs), etc.) to name a few, may be equipped with elastomeric endlesstracks which enhance their traction and floatation on soft, slipperyand/or irregular grounds (e.g., soil, mud, sand, ice, snow, etc.) onwhich they operate.

One type of elastomeric endless track comprises an inner side includinga plurality of drive/guide projections, commonly referred to as“drive/guide lugs”, which are spaced apart along its longitudinaldirection and used for driving and/or guiding the track around wheels ofa vehicle to which the track provides traction. Very often, a mainfactor reducing the track's useful life is wear or other deterioration(e.g., deformation) of the drive/guide lugs. For example, as they moverelative to the wheels of the vehicle, the drive/guide lugs come intocontact with (e.g., impact and/or rub or otherwise frictionally contact)one or more of these wheels and this contact can wear or otherwisedeteriorate (e.g., deform) their elastomeric material (e.g., rubber).Over time, such contact can wear or otherwise deteriorate thedrive/guide lugs, possibly to a point where the drive/guide lugs are sodeteriorated that the track can no longer be used efficiently and has tobe repaired or replaced. In some cases, such deterioration of thedrive/guide lugs can occur although a carcass of the track remains inacceptable condition. In other words, the drive/guide lugs candeteriorate at a significantly greater rate than the carcass of thetrack.

This type of track also comprises a ground-engaging outer side includinga plurality of traction projections, commonly referred to as “tractionlugs”, which are spaced apart along its longitudinal direction toenhance traction on the ground. Although it may be less severe than wearor other deterioration of the track's drive/guide lugs, wear or otherdeterioration of the traction lugs (e.g., due to particularly abrasiveground material) can sometimes become significant enough to forcereplacement of the track even though the track's carcass is still inacceptable condition.

For these and other reasons, there is a need to improve elastomericendless tracks for traction of vehicles and components of such tracks.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided an endlesstrack for traction of an off-road vehicle. The endless track ismountable around a plurality of wheels of the off-road vehicle. Theplurality of wheels comprises a drive wheel for driving the endlesstrack. The endless track comprises an elastomeric belt-shaped bodycomprising an inner surface for facing the wheels and a ground-engagingouter surface for engaging the ground. The endless track also comprisesa plurality of elastomeric drive/guide lugs projecting from the innersurface. Each elastomeric drive/guide lug of the plurality ofelastomeric drive/guide lugs has a material composition defining anarrangement of zones of different materials. The arrangement of zones ofdifferent materials comprises a plurality of zones of differentelastomeric materials. The elastomeric drive/guide lug exhibits adesired variation of a material property across the arrangement of zonesof different materials.

According to another aspect of the invention, there is provided anendless track for traction of an off-road vehicle. The endless track ismountable around a plurality of wheels of the off-road vehicle. Theplurality of wheels comprises a drive wheel for driving the endlesstrack. The endless track comprises an elastomeric belt-shaped bodycomprising an inner surface for facing the wheels and a ground-engagingouter surface for engaging the ground. The endless track also comprisesa plurality of traction lugs projecting from the ground-engaging outersurface. Each elastomeric traction lug of the plurality of elastomerictraction lugs has a material composition defining an arrangement ofzones of different materials. The arrangement of zones of differentmaterials comprises a plurality of zones of different elastomericmaterials. The elastomeric traction lug exhibits a desired variation ofa material property across the arrangement of zones of differentmaterials.

According to an aspect of the invention, there is provided an endlesstrack for traction of an off-road vehicle. The endless track ismountable around a plurality of wheels of the off-road vehicle. Theplurality of wheels comprises a drive wheel for driving the endlesstrack. The endless track comprises an elastomeric belt-shaped bodycomprising an inner surface for facing the wheels and a ground-engagingouter surface for engaging the ground. The endless track also comprisesa plurality of elastomeric lugs projecting from a given one of the innersurface and the ground-engaging outer surface. Each elastomeric lug ofthe plurality of elastomeric lugs has a material composition defining anarrangement of zones of different materials. The arrangement of zones ofdifferent materials comprises a plurality of zones of differentelastomeric materials. The elastomeric lug exhibits a desired variationof a material property across the arrangement of zones of differentmaterials.

According to another aspect of the invention, there is provided anendless track for traction of an off-road vehicle. The endless track ismountable around a plurality of wheels of the off-road vehicle. Theplurality of wheels comprises a drive wheel for driving the endlesstrack. The endless track comprises an elastomeric belt-shaped bodycomprising an inner surface for facing the wheels and a ground-engagingouter surface for engaging the ground. The endless track also comprisesa plurality of elastomeric drive/guide lugs projecting from the innersurface. Each elastomeric drive/guide lug of the plurality ofelastomeric drive/guide lugs comprises a plurality of zones of differentelastomeric materials. The elastomeric drive/guide lug exhibits anincrease of a modulus of elasticity inwardly.

According to another aspect of the invention, there is provided anendless track for traction of an off-road vehicle. The endless track ismountable around a plurality of wheels of the off-road vehicle. Theplurality of wheels comprises a drive wheel for driving the endlesstrack. The endless track comprises an elastomeric belt-shaped bodycomprising an inner surface for facing the wheels and a ground-engagingouter surface for engaging the ground. The endless track also comprisesa plurality of elastomeric drive/guide lugs projecting from the innersurface. Each elastomeric drive/guide lug of the plurality ofelastomeric drive/guide lugs comprises a first elastomeric material anda second elastomeric material stiffer than the first elastomericmaterial. The first elastomeric material is disposed between a peripheryof the elastomeric drive/guide lug and the second elastomeric material.

According to another aspect of the invention, there is provided a methodof making an endless track for traction of an off-road vehicle. Theendless track is mountable around a plurality of wheels of the off-roadvehicle. The plurality of wheels comprises a drive wheel for driving theendless track. The method comprises forming an elastomeric belt-shapedbody of the endless track. The elastomeric belt-shaped body comprises aninner surface for facing the wheels and a ground-engaging outer surfacefor engaging the ground. The method also comprises forming a pluralityof elastomeric lugs of the endless track which project from a given oneof the inner surface and the ground-engaging outer surface. Eachelastomeric lug of the plurality of elastomeric lugs has a materialcomposition defining an arrangement of zones of different materials. Thearrangement of zones of different materials comprises a plurality ofzones of different elastomeric materials. The elastomeric lug exhibits adesired variation of a material property across the arrangement of zonesof different materials.

According to another aspect of the invention, there is provided anendless track for traction of an off-road vehicle. The endless track ismountable around a plurality of wheels of the off-road vehicle. Theplurality of wheels comprises a drive wheel for driving the endlesstrack. The endless track comprises an elastomeric belt-shaped bodycomprising an inner surface for facing the wheels and a ground-engagingouter surface for engaging the ground. The endless track also comprisesa plurality of elastomeric lugs projecting from a given one of the innersurface and the ground-engaging outer surface. Each elastomeric lug ofthe plurality of elastomeric lugs has a material composition defining anarrangement of zones of different materials. The arrangement of zones ofdifferent materials comprises a sacrificial zone designed to besacrificed during use of the endless track.

According to another aspect of the invention, there is provided a methodof making an endless track for traction of an off-road vehicle. Theendless track is mountable around a plurality of wheels of the off-roadvehicle. The plurality of wheels comprises a drive wheel for driving theendless track. The method comprises forming an elastomeric belt-shapedbody of the endless track. The elastomeric belt-shaped body comprises aninner surface for facing the wheels and a ground-engaging outer surfacefor engaging the ground. The method also comprises forming a pluralityof elastomeric lugs of the endless track which project from a given oneof the inner surface and the ground-engaging outer surface. Eachelastomeric lug of the plurality of elastomeric lugs has a materialcomposition defining an arrangement of zones of different materials. Thearrangement of zones of different materials comprises a sacrificial zonedesigned to be sacrificed during use of the endless track.

According to another aspect of the invention, there is provided anendless track for traction of an off-road vehicle. The endless track ismountable around a plurality of wheels of the off-road vehicle. Theplurality of wheels comprises a drive wheel for driving the endlesstrack. The endless track comprises an elastomeric belt-shaped bodycomprising an inner surface for facing the wheels and a ground-engagingouter surface for engaging the ground. The endless track also comprisesa plurality of elastomeric lugs projecting from a given one of the innersurface and the ground-engaging outer surface. Each elastomeric lug ofthe plurality of elastomeric lugs has a material composition defining anarrangement of zones of different materials. The arrangement of zones ofdifferent materials comprises a wear indicator zone to indicate a levelof wear of the elastomeric lug.

According to another aspect of the invention, there is provided anendless track for traction of an off-road vehicle. The endless track ismountable around a plurality of wheels of the off-road vehicle. Theplurality of wheels comprises a drive wheel for driving the endlesstrack. The drive wheel comprises a plurality of drive members spacedapart from one another. The endless track comprises an elastomericbelt-shaped body comprising an inner surface for facing the wheels and aground-engaging outer surface for engaging the ground. The endless trackalso comprises a plurality of elastomeric drive lugs projecting from theinner surface and configured to engage the drive wheel. Each elastomericdrive lug of the plurality of elastomeric drive lugs comprises a drivesurface for contacting a drive member of the plurality of drive memberswhen the elastomeric drive lug engages the drive member. The drivesurface of the elastomeric drive lug is uneven such that an unevenportion of the elastomeric drive lug contacts the drive member when theelastomeric drive lug engages the drive member.

According to another aspect of the invention, there is provided anendless track for traction of an off-road vehicle. The endless track ismountable around a plurality of wheels of the off-road vehicle. Theplurality of wheels comprises a drive wheel for driving the endlesstrack. The drive wheel comprises a plurality of drive members spacedapart from one another. The endless track comprises an elastomericbelt-shaped body comprising an inner surface for facing the wheels and aground-engaging outer surface for engaging the ground. The endless trackalso comprises a plurality of elastomeric drive lugs projecting from theinner surface and configured to engage the drive wheel. Each elastomericdrive lug of the plurality of elastomeric drive lugs comprises a drivesurface for contacting a drive member of the plurality of drive memberswhen the elastomeric drive lug engages the drive member. The drivesurface of the elastomeric drive lug forming a protrusion of theelastomeric drive lug. The protrusion of the elastomeric drive lugextends towards and contacts the drive member when the elastomeric drivelug engages the drive member.

According to another aspect of the invention, there is provided a methodof making an endless track for traction of an off-road vehicle. Theendless track is mountable around a plurality of wheels of the off-roadvehicle. The plurality of wheels comprises a drive wheel for driving theendless track. The drive wheel comprises a plurality of drive membersspaced apart from one another. The method comprises forming anelastomeric belt-shaped body of the endless track. The elastomericbelt-shaped body comprises an inner surface for facing the wheels and aground-engaging outer surface for engaging the ground. The method alsocomprises forming a plurality of elastomeric drive lugs of the endlesstrack which project from the inner surface. Each elastomeric drive lugof the plurality of elastomeric drive lugs comprises a drive surface forcontacting a drive member of the plurality of drive members when theelastomeric drive lug engages the drive member. The drive surface of theelastomeric drive lug is uneven such that an uneven portion of theelastomeric drive lug contacts the drive member when the elastomericdrive lug engages the drive member.

These and other aspects of the invention will now become apparent tothose of ordinary skill in the art upon review of the followingdescription of embodiments of the invention in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of embodiments of the invention is providedbelow, by way of example only, with reference to the accompanyingdrawings, in which:

FIG. 1 shows an example of a tracked vehicle in accordance with anembodiment of the invention;

FIGS. 2 to 5 respectively show a outer plan view, a side view, an innerplan view, and a cross-sectional view of an example of an endless trackof a track assembly of the tracked vehicle;

FIG. 6A shows an example of an inner lug of the endless track;

FIG. 6B shows an example of an arrangement of zones of differentmaterials of an inner lug of the endless track;

FIG. 7 shows an example of a drive wheel of the track assembly;

FIG. 8 shows an example of an inner lug of the endless track engaging adrive member of the drive wheel;

FIG. 9 shows an example of an inner lug of the endless track betweenroller wheels of the track assembly;

FIGS. 10A to 11B, 13A, 13B, 14 to 18A, 19 and 20 show different examplesof an inner lug of the endless track having an arrangement of zones ofdifferent materials;

FIGS. 12A, 12B and 18B show different examples of a variation of amaterial property across an arrangement of different materials of aninner lug of the endless track;

FIGS. 21 and 22 show different examples of an uneven drive surface of adrive lug of the endless track facing a drive member of the drive wheel;and

FIG. 23 shows an example of an inner lug of the endless track designedto avoid interference with a roller wheel support of the track assembly.

It is to be expressly understood that the description and drawings areonly for the purpose of illustrating certain embodiments of theinvention and are an aid for understanding. They are not intended to bea definition of the limits of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 shows an example of an off-road tracked vehicle 10 in accordancewith an embodiment of the invention. In this embodiment, the vehicle 10is a heavy-duty work vehicle for performing agricultural work,construction or other industrial work, or military work. Moreparticularly, in this embodiment, the vehicle 10 is an agriculturalvehicle for performing agricultural work. Specifically, in this example,the agricultural vehicle 10 is a tractor. In other examples, theagricultural vehicle 10 may be a combine harvester, another type ofharvester, or any other type of agricultural vehicle.

The agricultural vehicle 10 comprises a frame 12 supporting a primemover 14, a pair of track assemblies 16 ₁, 16 ₂ (which can be referredto as “undercarriages”), and an operator cabin 20, which enable anoperator to move the agricultural vehicle 10 on the ground to performagricultural work possibly using a work implement 18.

The prime mover 14 provides motive power to move the agriculturalvehicle 10. For example, the prime mover 14 may comprise an internalcombustion engine and/or one or more other types of motors (e.g.,electric motors, etc.) for generating motive power to move theagricultural vehicle 10. The prime mover 14 is in a driving relationshipwith each of the track assemblies 16 ₁, 16 ₂. That is, power derivedfrom the prime mover 14 is transmitted to the track assemblies 16 ₁, 16₂ via a powertrain of the agricultural vehicle 10.

The work implement 18 is used to perform agricultural work. For example,in some embodiments, the work implement 18 may be a combine head, acutter, a scraper, a tiller or any other type of agricultural workimplement.

The operator cabin 20 is where the operator sits and controls theagricultural vehicle 10. More particularly, the operator cabin 20comprises a set of controls that allow the operator to steer theagricultural vehicle 10 on the ground and operate the work implement 18.

The track assemblies 16 ₁, 16 ₂ engage the ground to propel theagricultural vehicle 10. More particularly, in this embodiment, eachtrack assembly 16 _(i) comprises an endless track 22 disposed around aplurality of wheels, including a drive wheel 24 and a plurality of idlerwheels which includes a front idler wheel 26 and a plurality of rollerwheels 28 ₁-28 ₆. The track assembly 16 _(i) also comprises a frame 13which supports various components of the track assembly 16 _(i),including the roller wheels 28 ₁-28 ₆. The track assembly 16 _(i) has afirst longitudinal end 57 and a second longitudinal end 59 that define alength of the track assembly 16 _(i). A width of the track assembly 16_(i) is defined by a width of the endless track 22. The track assembly16 _(i) has a longitudinal direction, a widthwise direction, and aheight direction.

The endless track 22 engages the ground to provide traction to theagricultural vehicle 10. With additional reference to FIGS. 2 to 4, thetrack 22 has an inner side 45 facing the wheels 24, 26, 28 ₁-28 ₆ anddefining an inner area of the track 22 in which these wheels arelocated. The track 22 also has a ground-engaging outer side 47 oppositethe inner side 45 and engaging the ground on which the agriculturalvehicle 10 travels. The track 22 has a top run 65 which extends betweenthe longitudinal ends 57, 59 of the track assembly 16 _(i) and over thewheels 24, 26, 28 ₁-28 ₆ and a bottom run 66 which extends between thelongitudinal ends 57, 59 of the track assembly 16 _(i) and under thewheels 24, 26, 28 ₁-28 ₆. The track 22 has a longitudinal direction, awidthwise direction, and a thickness direction.

The endless track 22 comprises an elastomeric belt-shaped body 36underlying its inner side 45 and its ground-engaging outer side 47. Inview of its underlying nature, the belt-shaped body 36 can be referredto as a “carcass”. The carcass 36 is elastomeric in that it compriseselastomeric material 38 which allows the track 22 to elastically changein shape as it is in motion around the wheels 24, 26, 28 ₁-28 ₆. Theelastomeric material 38 can be any polymeric material with suitableelasticity. In this embodiment, the elastomeric material includesrubber.

Various rubber compounds may be used and, in some cases, differentrubber compounds may be present in different areas of the track 22. Inother embodiments, the elastomeric material 38 may include anotherelastomer in addition to or instead of rubber (e.g., polyurethaneelastomer).

As shown in FIG. 5, which is a cross-sectional view of track 22 takenalong line B-B in FIG. 2, in this embodiment, the carcass 36 comprises aplurality of reinforcements 42, 43 embedded in its elastomeric material38. In this example, the reinforcement 42 is a layer of reinforcingcables that are adjacent to one another and that extend in thelongitudinal direction of the track 22 to enhance strength in tension ofthe track 22 along its longitudinal direction. In some cases, areinforcing cable may be a cord or wire rope including a plurality ofstrands or wires. In other cases, a reinforcing cable may be anothertype of cable and may be made of any material suitably flexiblelongitudinally (e.g., fibers or wires of metal, plastic or compositematerial). The reinforcement 43 is a layer of reinforcing fabric.Reinforcing fabric comprises pliable material made usually by weaving,felting, or knitting natural or synthetic fibers. For instance, a layerof reinforcing fabric may comprise a ply of reinforcing woven fibers(e.g., nylon fibers or other synthetic fibers). Various other types ofreinforcements may be provided in the carcass 36 in other embodiments.

The ground-engaging outer side 47 comprises a ground-engaging outersurface 75 of the carcass 36 and a tread pattern 40 to enhance tractionon the ground. The tread pattern 40 comprises a plurality of tractionprojections 58 ₁-58 _(T), which will be referred to as “traction lugs”,projecting from the ground-engaging outer surface 75, spaced apart alongthe longitudinal direction of the endless track 22 and engaging theground to enhance traction. In this embodiment, each of the tractionlugs 58 ₁-58 _(T) has an elongated shape and is angled, i.e., defines anoblique angle θ (i.e., an angle that is not a right angle or a multipleof a right angle), relative to the longitudinal direction of the endlesstrack 22. The traction lugs 58 ₁-58 _(T) may have various other shapesin other examples (e.g., curved shapes, shapes with straight parts andcurved parts, etc.).

In this embodiment, each traction lugs 58 ₁ is an elastomeric tractionlug in that it comprises elastomeric material 41. The elastomericmaterial 41 can be any polymeric material with suitable elasticity. Moreparticularly, in this embodiment, the elastomeric material 41 includesrubber. Various rubber compounds may be used and, in some cases,different rubber compounds may be present in different areas of thetraction lug 58 _(i). In other embodiments, the elastomeric material 41may include another elastomer in addition to or instead of rubber (e.g.,polyurethane elastomer). The traction lugs 58 ₁-58 _(T) may be providedon the ground-engaging outer side 27 in various ways. For example, inthis embodiment, the traction lugs 58 ₁-58 _(T) are provided on theground-engaging outer side 27 by being molded with the carcass 36.

The inner side 45 of the endless track 22 comprises an inner surface 55of the carcass 36 and a plurality of inner wheel-contacting projections48 ₁-48 _(N) that project from the inner surface 55 and are positionedto contact at least some of the wheels 24, 26, 28 ₁-28 ₆ to do at leastone of driving (i.e., imparting motion to) the track 22 and guiding thetrack 22. The wheel-contacting projections 48 ₁-48 _(N) can be referredto as “wheel-contacting lugs”. Furthermore, since each of them is usedto do at least one of driving the track 22 and guiding the track 22, thewheel-contacting lugs 48 ₁-48 _(N) can be referred to as “drive/guideprojections” or “drive/guide lugs”. In some examples of implementation,a drive/guide lug 48 _(i) may interact with the drive wheel 24 to drivethe track 22, in which case the drive/guide lug 48 _(i) is a drive lug.In other examples of implementation, a drive/guide lug 48 _(i) mayinteract with the idler wheel 26 and/or the roller wheels 28 ₁-28 ₆ toguide the track 22 to maintain proper track alignment and preventde-tracking without being used to drive the track 22, in which case thedrive/guide lug 48 _(i) is a guide lug. In yet other examples ofimplementation, a drive/guide lug 48 _(i) may both (i) interact with thedrive wheel 24 to drive the track and (ii) interact with the idler wheel26 and/or the roller wheels 28 ₁-28 ₆ to guide the track 22 to maintainproper track alignment and prevent de-tracking, in which case thedrive/guide lug 48 _(i) is both a drive lug and a guide lug.

In this embodiment, the drive/guide lugs 48 ₁-48 _(N) interact with thedrive wheel 24 in order to cause the track 22 to be driven, and alsointeract with the idler wheel 26 and the roller wheels 28 ₁-28 ₆ inorder to guide the track 22 as it is driven by the drive wheel 24 tomaintain proper track alignment and prevent de-tracking. The drive/guidelugs 48 ₁-48 _(N) are thus used to both drive the track 22 and guide thetrack 22 in this embodiment.

In this example of implementation, the drive/guide lugs 48 ₁-48 _(N) arearranged in a single row disposed longitudinally along the inner side 45of the track 22. The drive/guide lugs 48 ₁-48 _(N) may be arranged inother manners in other examples of implementation (e.g., in a pluralityof rows that are spaced apart along the widthwise direction of the track22).

The drive/guide lugs 48 ₁-48 _(N) may have any suitable shape. Withadditional reference to FIG. 6, each drive/guide lug 48 _(i) has aperiphery 69 which, in this embodiment, includes a front surface 80 ₁, arear surface 80 ₂, two side surfaces 81 ₁, 81 ₂, and a top surface 86.The front surface 80 ₁ and the rear surface 80 ₂ are opposed to oneanother along the longitudinal direction of the track 22. In thisembodiment where the drive/guide lug 48 _(i) is used to drive the track22, each of the front surface 80 ₁ and the rear surface 80 ₂ constitutesa drive surface which can be contacted by a drive member of the drivewheel 24 that pushes against it to impart motion to the track 22. Thetwo side faces 81 ₁, 81 ₂ are laterally opposed and may contact theroller wheels 28 ₁-28 ₆, the drive wheel 24 and/or the idler wheel 26such as to prevent excessive lateral movement of the track 22 relativethe wheels and to thus prevent de-tracking. Although it has a certainshape in this embodiment, the periphery 70 of the drive/guide lug 48_(i) may have various other shapes in other embodiments.

Each drive/guide lug 48 _(i) has a front-to-rear dimension L_(L) in thelongitudinal direction of the endless track 22 and a side-to-sidedimension L_(W) in the widthwise direction of the endless track 22. Insome cases, the front-to-rear dimension L_(L) may be a width of thedrive/guide lug 48 _(i) while the side-to-side dimension L_(W) may be alength of the drive/guide lug 48 _(i). In other cases, the front-to-reardimension L_(L) may be a length of the drive/guide lug 48 _(i) while theside-to-side dimension L_(W) may be a width of the drive/guide lug 48_(i). In yet other cases, the front-to-rear dimension L_(L) and theside-to-side dimension L_(W) may be substantially the same. Thedrive/guide lug 48 _(i) also has a height H.

In this embodiment, each drive/guide lug 48 _(i) is an elastomericdrive/guide lug in that it comprises elastomeric material 67. Theelastomeric material 67 can be any polymeric material with suitableelasticity. More particularly, in this embodiment, the elastomericmaterial 67 includes rubber. Various rubber compounds may be used and,in some cases, different rubber compounds may be present in differentareas of the drive/guide lug 48 _(i). In other embodiments, theelastomeric material 67 may include another elastomer in addition to orinstead of rubber (e.g., polyurethane elastomer). The drive/guide lugs48 ₁-48 _(N) may be provided on the inner side 45 in various ways. Forexample, in this embodiment, the drive/guide lugs 48 ₁-48 _(N) areprovided on the inner side 45 by being molded with the carcass 36.

The endless track 22 may be constructed in various other manners inother embodiments. For example, in some embodiments, the track 22 maycomprise a plurality of elastomeric sections (e.g., rubber sections)connected to one another to form the belt-shaped body 36, the track 22may have recesses or holes that interact with the drive wheel 24 inorder to cause the track 22 to be driven (e.g., in which case thedrive/guide lugs 48 ₁-48 _(N) may be used only to guide the track 22without being used to drive the track 22, i.e., they may be “guide lugs”only), and/or the ground-engaging outer side 47 of the track 22 maycomprise various patterns of traction lugs.

The drive wheel 24 is rotatable by power derived from the prime mover 14to drive the track 22. That is, power generated by the prime mover 14and delivered over the powertrain of the agricultural vehicle 10 canrotate a driven axle, which causes rotation of the drive wheel 24, whichin turn imparts motion of the track 22.

With additional reference to FIG. 7, in this embodiment, the drive wheel24 comprises a drive sprocket comprising a plurality of drive members 52₁-52 _(B) spaced apart along a circular path to engage the drive/guidelugs 48 ₁-48 _(N) of the track 22 in order to drive the track 22. Thedrive wheel 24 and the track 22 thus implement a “positive drive”system. More particularly, in this embodiment, the drive wheel 24comprises two side discs 50 ₁, 50 ₂ which are co-centric and turn abouta common axle 51 and between which the drive members 52 ₁-52 _(B) extendnear respective peripheries of the side discs 50 ₁, 50 ₂. In thisexample, the drive members 52 ₁-52 _(B) are thus drive bars that extendbetween the side discs 50 ₁, 50 ₂. The drive wheel 24 and the track 22have respective dimensions allowing interlocking of the drive bars 52₁-52 _(B) of the drive wheel 24 and the drive/guide lugs 48 ₁-48 _(N) ofthe track 22. Adjacent ones of the drive bars 52 ₁-52 _(B) define aninterior space 53 between them to receive one of the drive/guide lugs 48₁-48 _(N). Adjacent ones of the drive/guide lugs 48 ₁-48 _(N) define aninter-lug space 37 between them to receive one of the drive bars 52 ₁-52_(B). The drive/guide lugs 48 ₁-48N and the drive bars 52 ₁-52 _(B) havea regular spacing that allows interlocking of the drive/guide lugs 48₁-48 _(N) and the drive bars 52 ₁-52 _(B) over a certain length of thedrive wheel's circumference.

The drive wheel 24 may be configured in various other ways in otherembodiments. For example, in other embodiments, the drive wheel 24 maynot have any side discs such as the side discs 50 ₁, 50 ₂. As anotherexample, in other embodiments, instead of being drive bars, the drivemembers 52 ₁-52 _(B) may be drive teeth that are distributedcircumferentially along the drive wheel 24 or any other type of drivemembers. As another example, in embodiments where the track 22 comprisesrecesses or holes, the drive wheel 24 may have teeth that enter theserecesses or holes in order to drive the track 22. As yet anotherexample, in some embodiments, the drive wheel 24 may frictionally engagethe inner side 45 of the track 22 in order to frictionally drive thetrack 22 (i.e., the drive wheel 24 and the track 22 may implement a“friction drive” system).

The front idler wheel 26 and the roller wheels 28 ₁-28 ₆ are not drivenby power supplied by the prime mover 14, but are rather used to do atleast one of supporting part of the weight of the agricultural vehicle10 on the ground via the track 22, guiding the track 22 as it is drivenby the drive wheel 24, and tensioning the track 22. More particularly,in this embodiment, the front idler wheel 26 is a leading idler wheelwhich maintains the track 22 in tension and helps to support part of theweight of the agricultural vehicle 10 on the ground via the track 22.The roller wheels 28 ₁-28 ₆ roll on a rolling path 33 of the inner side45 of the track 22 along the bottom run 66 of the track 22 to apply thebottom run 66 on the ground. In this case, as they are located betweenfrontmost and rearmost ones of the wheels of the track assembly 16 _(i),the roller wheels 28 ₁-28 ₆ can be referred to as “mid-rollers”.

The drive/guide lugs 48 ₁-48 _(N) are susceptible to wear or otherdeterioration, notably due to their motion relative to the wheels 24,26, 28 ₁-28 ₆. For example, in some cases, as the drive/guide lugs 48₁-48 _(N) contact the drive wheel 24, forces exerted on the lugs 48 ₁-48_(N) create stresses in them which may tend to wear or otherwisedeteriorate them. As another example, in some cases, friction betweenthe drive/guide lugs 48 ₁-48 _(N) and the mid-rollers 28 ₁-28 ₆ may alsoinduce wear of the lugs 48 ₁-48 _(N) and/or the mid-rollers 28 ₁-28 ₆.

Various forces and effects may contribute to the wear or otherdeterioration of drive/guide lugs 48 ₁-48 _(N). For example, in variouscases, loads applied on the drive/guide lugs 48 ₁-48 _(N) (e.g., by thedrive wheel 24 and/or mid-rollers 28 ₁-28 ₆) and/or ingestion of debris(e.g., rocks or other ground matter) within the track assembly 16 _(i)may cause crack initiation and propagation, abrasion, tearing and/oreffects tending to wear or otherwise deteriorate the drive/guide lugs 48₁-48 _(N). Examples of such factors will be discussed below forillustrative purposes, without wishing to be bound by theory.

For instance, FIG. 8 is a cross-sectional view of a drive/guide lug 48_(i) taken along line C-C of FIG. 4, but shown positioned in theinterior space 53 adjacent to a drive bar 52 _(j) of the drive wheel 24.When, in motion, the drive/guide lug 48 _(i) received within theinterior space 53 is contacted by the drive bar 52 _(j) on its frontsurface 80 ₁, the drive bar 52 _(j) pushes against the front surface 80₁ and applies thereto a force F_(M). The force F_(M) causes thedrive/guide lug 48 _(i) to move with the drive bar 52 _(j), which inturn causes the whole track 22 to move within the track assembly 16_(i). Although only the lug 48 _(i) is being discussed here, multipleones of the drive/guide lugs 48 ₁-48 _(N) may be in interlock with thedrive sprocket 24 at any given time so that the cumulative forcesapplied on all those lugs interlocked with the sprocket 24 combine tocause the motion of the track 22. The force F_(M) may not be constantbut may vary depending on the position of the drive/guide lug 48 _(i)within the sprocket 24, and is applied only while the drive/guide lug 48_(i) is in contact with the sprocket 24.

The force F_(M) applied to the drive/guide lug 48 _(i) may cause variousstrains on the drive/guide lug 48 _(i). For example, the force F_(M)applied to the drive/guide lug 48 _(i) may cause a compressive strain ina region R1 of the drive/guide lug 48 _(i) proximate its front surface80 ₁. In certain instances, the drive/guide lug 48 _(i) may deform underthe force F_(M), such as by bending in the direction of the force F_(M).Such bending causes a compressive strain in a region R2 of thedrive/guide lug 48 _(i) and tensile strain in a region R3 of thedrive/guide lug 48 _(i).

Repeated deformation of the drive/guide lug 48 _(i), possibly combinedwith friction on the drive/guide lug 48 _(i), causes heat to begenerated within the drive/guide lug 48 _(i). This heat may changeproperties of a material making up part or all of the drive/guide lug 48_(i), such as an elastic modulus, a hardness, an abrasion resistance,etc., causing it to be less suited for resisting the forces applied onthe drive/guide lug 48 _(i). Over time, if the heat generated isexcessive, this may cause premature ageing of a materials making up partor all of the drive/guide lug 48 _(i), therefore limiting the elasticityof material that can be used. On the other hand, if a material is toorigid, stresses in the drive/guide lug 48 _(i), such as tensile stressesin the region R3, may cause the drive/guide lug 48 _(i) to crack, and/orbrittleness effects may arise.

Due to loads, material properties or changes in material properties,and/or hysteresis effects, in some cases, the drive/guide lug 48 _(i)may also become deformed in such a way that it loses a desired shapewith which it was designed. This may lead to additional stresses (e.g.from increased rubbing and compression in the track assembly 16) whichin turn may lead to further hastened wearing. For instance, thisdeformation may reduce a clearance between the drive/guide lug 48 _(i)in contact with the sprocket bar 52 _(j) and the following sprocket bar52 _(k), possibly to a point where there can be interference between thesprocket bar 52 _(k) and the drive/guide lug 48 _(i). In such cases, themovement of the sprocket bar 52 _(k) relative to the drive/guide lug 48_(i) would generate a scrubbing force on a portion of the face of thedrive/guide lug 48 _(i). A pitch between consecutive ones of thedrive/guide lugs 48 ₁-48 _(N) may be altered (e.g., increased) comparedto its designed value.

The drive/guide lug 48 _(i) may also crack. For instance, due tomanufacturing or material imperfections or simply age, tension in thedrive/guide lug 48 _(i) may cause the drive/guide lug 48 _(i) to crack.Cracks may also develop in the absence of induced weaknesses if, forexample, an excessive applied force causes a tensile stress in thedrive/guide lug 48 _(i) that is higher than a certain threshold.

Debris, such as rocks, mud, dirt, or other foreign matter ingestedwithin the track assembly 16 _(i), may contact and rub against thedrive/guide lug 48 _(i). In particular, if debris enters the drive wheel24, and more particularly if it comes between the sprocket bar 52 _(j)and the drive/guide lug 48 _(i), the front face 80 of the drive/guidelug 48 _(i) may be subject to abrasion or chunking, particularly in theregion R1.

FIG. 9 is a cross-sectional view of the drive/guide lug 48 _(i) takenalong line D-D of FIG. 4 but shown between mid-rollers 28 _(i), 28 _(j)that laterally face adjacent one another. The lateral spacing of themid-rollers 28 _(i), 28 _(j) may be greater than the width of thedrive/guide lug 48 _(i) to provide a clearance between the drive/guidelug 48 _(i) and the mid-rollers 28 _(i), 28 _(j).

The mid-roller 28 _(i) is adapted to rotate about an axle 94. Themid-roller 28 _(i) has a peripheral portion 91 adjacent the inner side45 of the track 22 and a body portion between the axle 94 and theperipheral portion 91. The peripheral portion 91 of the mid-roller 28_(i) has a peripheral surface 92 to roll on the inner side 45 of thetrack 22. The mid-roller 28 _(i) also has an inner lateral surface 93adjacent the side surface 81 ₁ of the drive/guide lug 48 _(i).

In use, the drive/guide lug 48 _(i) may contact the mid-roller 28 _(i)(e.g., due to track misalignment or loading on the track assembly 16_(i) causing lateral movement of the mid-roller 28 _(i)). This causesthe mid-roller 28 _(i) to exert a force F_(L) on the drive/guide lug 48_(i). The force F_(L) may cause compression of a region R4 of thedrive/guide lug 48 _(i). Depending on the shape of the drive/guide lug48 _(i) and/or the mid-roller 28 _(i), the region R4 where the bulk ofthe force F_(L) is absorbed may vary in location. For instance, in thisexample, the region R4 is near the lower portion of the drive/guide lug48 _(i), adjacent the peripheral portion 91 of the mid-roller 28 _(i).

Compression in the region R4 may also result in tension elsewhere in thedrive/guide lug 48 _(i), such as in a region R6. Compression, such ascompression in the region R4, and tension, such as in the region R6, mayresult in similar deleterious effects on the drive/guide lug 48 _(i) asthose described above.

As the force F_(L) presses the region R4 towards the inner surface 93 ofthe mid-roller 28 _(i), additional areas of the side surface 81 ₁ of thedrive/guide lug 48 _(i) may come in contact and/or press against theinner lateral surface 93 of the mid-roller 28 _(i). For example, aportion of the drive/guide lug 48 _(i) may contact the inner lateralsurface 93 of the mid-roller 28 _(i) adjacent the mid portion 95thereof. This may be caused, for instance, by the contraction of thedrive/guide lug 48 _(i) in the region R4, resulting in the flattening ofthe angled profile of the side surface 81 ₁ into a more vertical profileor by the twisting or bending of the track 22. Alternatively, this maysimply be caused by the geometry of the drive/guide lug 48 _(i) and/orthe geometry of the mid-roller 28 _(i).

When the mid-roller 28 _(i) turns about its axel 94 and rolls on theinner side 45 of the endless track 22, there is a difference in velocitybetween respective points of the drive/guide lug 48 _(i) and themid-roller 28 _(i) which face one another. More particularly, since theentire drive/guide lug 48 _(i) moves at approximately the same velocity,and since the mid-roller 28 _(i) has a tangential velocity which variesacross its radius, even if the tangential velocity of the mid-roller 28_(i) matches the velocity of the drive/guide lug 48 _(i) at a particulardistance from the mid-roller's center (namely, at the peripheral surface92 of the mid-roller 28 _(i) which contacts the rolling path 33 of thetrack 22), the tangential velocity of the mid-roller 28 _(i) will notmatch the velocity of the drive/guide lug 48 _(i) elsewhere along themid-roller's radius. The greater the radial distance from the point ofmatched velocities, the greater the relative difference between thetangential velocity of the mid-roller 28 _(i) and the drive/guide lug 48_(i) will be.

A region R5 represents a region where contact may occur between the sidesurface 81 ₁ of the drive/guide lug 48 _(i) and the inner lateralsurface 93 of the mid-roller 28 _(i) where the velocity of thedrive/guide lug 48 _(i) and the tangential velocity of the mid-roller 28_(i) are not matched. The tangential velocity of the mid-roller 28 _(i)where the region R5 is located is smaller than the velocity of thedrive/guide lug 48 _(i). Due to a difference in velocities between theside surface 81 ₁ of the drive/guide lug 48 _(i) and the inner lateralsurface 93 of the mid-roller 28 _(i) in the region R5, the region R5 issubject to friction. This friction may cause generation of heat in theregion R5, causing the deleterious effects of heat mentioned above.Furthermore, the friction at the region R5 may also cause theaccelerated wearing of the drive/guide lug 48 _(i) at that region.

While the above example relates to the interaction between thedrive/guide lug 48 _(i) and the mid-roller 28 _(i), a similarinteraction may take place when the drive/guide lug 48 _(i) contacts thelaterally-opposite mid-roller 28 _(j). Also, while the above exampletakes into account only a single mid-roller, similar forces or othereffects may be experienced by the drive/guide lug 48 _(i) as it contactsother wheels, such as other ones of the mid-rollers 28 ₁-28 ₈, the frontidler wheel 26 or the drive wheel 24. As such, the geometry and/orlocation of the various regions of the drive/guide lug 48 _(i) discussedherein may vary depending upon the other wheels that the drive/guide lug48 _(i) contacts.

The above examples of forces and other effects on the drive/guide lug 48_(i) and of the regions affected by such forces and other effects arepresented for purposes of illustration only and should not beinterpreted in any limiting way since there may be a large number offorces and other effects affecting drive/guide lugs 48 ₁-48 _(N) thatmay depend upon a wide variety of factors.

Determination of regions of the drive/guide lugs 48 ₁-48 _(N) undergoingparticular stresses, strains and other effects (e.g., compression,tension, shear, friction, heating, abrasion, chunking, etc.) can be doneby various tests and/or analysis techniques (e.g., painting adrive/guide lug 48 _(i) to identify contact areas with the wheels 24,26, 28 ₁-28 ₈; placing load cells on a drive/guide lug 48 _(i) tomeasure loads in different regions; performing finite element analysis(FEA) or other computational analysis on a virtual model of adrive/guide lug 48 _(i); etc.).

In order to address their susceptibility to wear or other deterioration,the drive/guide lugs 48 ₁-48 _(N) can be designed to enhance theirresistance to wear or other deterioration or otherwise enhance theirperformance. This can be achieved in various ways in variousembodiments, examples of which will now be discussed.

1. Drive/Guide Lug with a Material Distribution Profile

In some embodiments, a drive/guide lug 48 _(i) may be characterized by amaterial distribution profile to enhance its resistance to wear or otherdeterioration or otherwise enhance its performance. With additionalreference to FIG. 6B, the material distribution profile is designed suchthat the drive/guide lug 48 _(i) has a material composition defining anarrangement of zones 105 ₁-105 _(Z) of different materials. Differentmaterials are materials which belong to different classes of materials(i.e., metals, polymers, ceramics and composites) and/or which exhibitsubstantially different values of a given material property (e.g., amodulus of elasticity, tensile strength, hardness, friction coefficient,crack growth resistance, etc.). The arrangement of zones 105 ₁-105 _(Z)is designed into the drive/guide lug 48 _(i). That is, the arrangementof zones 105 ₁-105 _(Z) does not occur by chance (e.g., duringmanufacturing or use of the drive/guide lug 48 _(i)), but is ratherachieved by a careful material selection and distribution within thedrive/guide lug 48 _(i) during design of the endless track 22.

The arrangement of zones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i)may be provided for various purposes. For example, in some embodiments,the arrangement of zones 105 ₁-105 _(Z) may be provided to create adesired variation in one or more material properties (e.g., modulus ofelasticity) across the drive/guide lug 48 _(i). As another example, insome embodiments, one or more of the zones 105 ₁-105 _(Z) may beprovided to implement a dedicated function, such as a wear indicator toindicate a level of wear of the drive/guide lug 48 _(i) or a sacrificialpiece used during break-in of the endless track 22. Examples of thearrangement of zones 105 ₁-105 _(Z) in various embodiments are discussedbelow.

The zones 105 ₁-105 _(Z) of the material distribution profile of thedrive/guide lug 48 _(i) may be provided in any suitable way using one ormore manufacturing processes, such as, for example, a molding process(e.g., an injection molding process, a compression molding process,etc.), an extrusion process (e.g., a coextrusion process), a pouringprocess, a gluing process, a coating process, a heat treatment, apenetrating treatment (e.g., an electromagnetic radiation treatment,etc.), and/or any other suitable manufacturing process. Examples of howthe zones 105 ₁-105 _(Z) may be provided in various embodiments arediscussed below.

The arrangement of zones 105 ₁-105 _(Z) may comprise two, three, four,five or more zones of different materials, as further discussed below.Also, while the arrangement of zones 105 ₁-105 _(Z) may comprise anyselection of different materials, in some embodiments, the arrangementof zones 105 ₁-105 _(Z) may comprise a plurality of zones of differentelastomeric materials (i.e., two, three, four, five or more zones ofdifferent elastomeric materials). For example, such differentelastomeric materials may include different rubbers, thermoplasticelastomers (TPE) such as polyurethane elastomers, and/or otherelastomers.

a) Property Variation Profile

In some embodiments, the arrangement of zones 105 ₁-105 _(Z) may beconfigured such that the drive/guide lug 48 _(i) exhibits a desiredproperty variation profile, i.e., a desired variation of one or morematerial properties across the arrangement of zones 105 ₁-105 _(Z). Thisvariation of one or more material properties is “desired” in that it isdesigned into the drive/guide lug 48 _(i) by the careful materialselection and distribution within the drive/guide lug 48 _(i) to createthe arrangement of zones 105 ₁-105 _(Z) during design of the endlesstrack 22 such that a material property varies in an intended manner. Inthat sense, this desired variation of one or more material propertiescan also be referred to as a “selected”, “predetermined”, “intended” or“controlled” variation of one or more material properties.

An example of a material property is a modulus of elasticity. For apurely elastic material, the modulus of elasticity can be taken as anelastic modulus (e.g., Young's modulus) of the material. For aviscoelastic material, the modulus of elasticity can be taken as a“complex modulus” of the material, which has two components: a storagemodulus E′, which relates to the material's elastic behavior and thus toenergy stored in the material under stress; and a loss modulus E″, whichrelates to the material's viscous behavior and thus to energy dissipatedby the material as heat under stress. The complex modulus may beevaluated using dynamic mechanical analysis (DMA) (e.g., based on astandard test such as ATSM D4065, D4440 or D5279). The magnitude of thecomplex modulus may be evaluated as the square root of the sum of thesquares of its components, i.e., ≈(E′²⁺ E″²). The complex modulus iswell known and will therefore not be discussed further.

Other examples of material properties include a hardness, a strength(e.g., a tensile strength, a compressive strength, a shear strength, ayield strength, or a fatigue strength), an abrasion resistance, a crackgrowth resistance such as a crack growth rate (e.g., in mm per number ofcycles, evaluated for instance using a pure-shear crack growth test), acoefficient of friction relative to another material, a heatconductivity, a coefficient of thermal expansion, a mass density, color,a resistance to degradation from UV or other radiation, etc. Variousother mechanical, thermal, electrical or optical properties may beconsidered in other cases. Other types of properties such asself-healing qualities may also be considered material properties andmay confer a particular characteristic to a zone 105 ₁.

A material property may be substantially constant over a useful life ofthe drive/guide lug 48 _(i). Alternatively, a material property may varyaccording to a variation of one or more physical parameters and/or mayvary over time. For example, a particular material may be characterizedby a particular modulus of elasticity that is substantially constant,while another material may be characterized by a modulus of elasticitythat varies as a function of temperature, age or other factors. In somecases, a material property may temporarily change as a function of aphysical parameter. In other cases, a material property may permanentlychange as a function of a physical parameter and/or time (e.g. amaterial that hardens over time, a material whose modulus of elasticitypermanently changes if a certain temperature is reached, etc.). Amaterial property can thus be considered or measured when the endlesstrack 22 is new and ready to be used on the vehicle 10 under normaloperating conditions in which the track 22 is expected to be used.

For purposes of example, in embodiments discussed below, the propertyvariation profile defined by the material distribution profile of thedrive/guide lug 48 _(i) includes a variation of the modulus ofelasticity across the arrangement of zones 105 ₁-105 _(Z) of thedrive/guide lug 48 _(i).

For instance, in some embodiments, the modulus of elasticity mayincrease inwardly, i.e., in a direction towards an inmost point of thedrive/guide lug 48 _(i). For example, in some cases, an outer zone ofthe drive/guide lug 48 _(i) may have a lower modulus of elasticity(i.e., higher elasticity) than an inner zone of the drive/guide lug 48_(i). Thanks to the low modulus of elasticity near the periphery of thedrive/guide lug 48 _(i), compressive forces applied on the drive/guidelug 48 _(i), for instance by the drive bars 52 ₁-52 _(B) of the drivewheel 24 and/or by the mid-rollers 28 ₁-28 ₈, may be absorbed by elasticdeformation of the drive/guide lug 48 _(i) near its exterior by thehigher elasticity of the material of the drive/guide lug 48 _(i) nearits exterior. This may prevent or at least impede crack propagationwithin the drive/guide lug 48 _(i) by reducing a potential for crackpropagation within the drive/guide lug 48 _(i). While absorption of theimpact and/or compressive forces applied to the drive/guide lug 48 _(i)may reduce cracking potential, excessive deformation of the drive/guidelug 48 _(i) may cause excessive strain on the drive/guide lug 48 _(i)that may lead to other problems. The higher modulus of elasticity of thematerial deeper within the drive/guide lug 48 _(i) serves to rigidifythe drive/guide lug 48 _(i) and thus prevent excessive deformationthereof. This may therefore further prevent or at least impede crackingand/or other negative effects.

While in embodiments discussed below the property variation profiledefined by the material distribution profile includes a variation of themodulus of elasticity across the arrangement of zones 105 ₁-105 _(Z) ofthe drive/guide lug 48 _(i), the property variation profile may includea variation of one or more other material properties in addition to orinstead of a variation of the modulus of elasticity in otherembodiments. Examples of such other material properties are mentionedabove.

The property variation profile defined by the arrangement of zones 105₁-105 _(Z) of the drive/guide lug 48 _(i) may be configured in variousways. For example, in various embodiments, the property variationprofile may include one or more gradients of modulus of elasticityacross three or more zones, where each gradient can be a discretegradient or a continuous gradient.

i. Discrete Gradient

In some embodiments, the property variation profile defined by thearrangement of zones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i) mayinclude a discrete gradient of modulus of elasticity. A discretegradient of modulus of elasticity is a discrete variation of the modulusof elasticity in a specified direction across the arrangement of zones105 ₁-105 _(Z) of the drive/guide lug 48 _(i). In such embodiments,adjacent ones of the zones 105 ₁-105 _(Z) which define the discretegradient of modulus of elasticity are discrete zones such that themodulus of elasticity varies in discrete steps across the drive/guidelug 48 _(i). A zone is “discrete” in that its dimension along thespecified direction of the discrete gradient is macroscopicallymeasurable.

For example, FIGS. 10A and 10B show an example of an embodiment in whichthe modulus of elasticity varies in discrete steps such that the zones105 ₁-105 _(Z) have different modulus of elasticity values.

In this embodiment, the arrangement of zones 105 ₁-105 _(Z) includes anouter zone 110, a mid zone 115, an inner zone 120 and a core zone 125.The mid zone 115, the inner zone 120 and the core zone 125 are entirelycontained within the drive/guide 48 _(i) lug such that each of the midzone 115, the inner zone 120 and the core zone 125 is spaced from theperiphery of the drive/guide lug 48 _(i). The outer zone 110 is disposedover and astride the mid-zone 115 which is beneath the outer zone 110,and the mid-zone 115 is disposed over and astride the inner zone 120which is beneath the mid-zone 115. In this example, each of the zones110, 115 comprises a top portion and a plurality of side portions thatextend from the top portion, terminate adjacent to a base of thedrive/guide lug 48 _(i) and contain therebetween a respective one of thezones 115, 120 that is beneath it. The side portions of the mid zone115, the inner zone 120 and the core zone 125 respectively extendsubstantially parallel to side surfaces of the drive/guide lug 48 _(i).The top portion of each of the mid zone 115, the inner zone 120 and thecore zone 125, extends substantially parallel to a top surface of thedrive/guide lug 48 _(i). In this example, each of the zones 110, 115 isshaped substantially as a scaled-down version of the periphery of thedrive/guide lug 48 _(i), and/or is generally U-shaped in a cross-sectionof the drive/guide lug 48 _(i) taken in the longitudinal direction ofthe track 22. In this example, the outer zone 110 terminates within thedrive/guide lug 48 _(i) in the cross-section of the drive/guide lug 48_(i) taken in the longitudinal direction of the track 22. In thisexample, the outer zone 110 has a lower modulus of elasticity (i.e., ahigher elasticity) than the mid zone 115, which has a lower modulus ofelasticity than the inner zone 120, which has a lower modulus ofelasticity than the core zone 125. Thus, the compressive forces appliedto the outside of the drive/guide lug 48 _(i) can be absorbed by elasticdeformation of the outer zone 110 and the mid zone 115 while the innerzone 120 and the core zone 125 can provide more rigidity.

For instance, in some embodiments, the outer zone 110, the mid zone 115,the inner zone 120 and the core zone 125 may be made of differentelastomeric materials (e.g., rubbers, thermoplastic elastomers (TPE)such as polyurethane elastomers, and/or other elastomers).

The elastomeric material of the outer zone 110 has a lower modulus ofelasticity than the elastomeric material of the mid zone 115. Thus, theelastomeric material of the outer zone 110 is more elastic (i.e., hasgreater elasticity) than the elastomeric material of the mid zone 115and is disposed between the periphery of the drive/guide lug 48 _(i) andthe elastomeric material of the mid zone 115. Conversely, theelastomeric material of the mid zone 115 is stiffer than the elastomericmaterial of the outer zone 110 and is disposed behind the elastomericmaterial of the outer zone 110.

The elastomeric material of the outer zone 110 is susceptible toelastically deforming upon application of a force, such as bycontracting inwards thereby absorbing part of the applied force. Thismay prevent or at least impede crack propagation within the drive/guidelug 48 _(i) (e.g., when it contacts the sprocket bars 52 ₁-52 _(B) ofthe drive wheel 24). Also, since it is exposed to the wheels 24, 26, 28₁-28 ₆ and the environment of the track assembly 16 _(i), theelastomeric material of the outer zone 110 may have a lower coefficientof friction with the wheels 24, 26, 28 ₁-28 ₆ and/or a higher abrasionresistance than the elastomeric material of the mid zone 115. Forinstance, in some cases, the elastomeric material of the outer zone 110may be a polyurethane elastomer.

While the modulus of elasticity of the elastomeric material of the outerzone 110 may be lower than that of the elastomeric material of the midzone 115 in some embodiments, this may not be the case in otherembodiments (e.g., in embodiments in which the outer zone 110 is basedon a polyurethane elastomer which does not necessarily have a lowermodulus of elasticity than the elastomeric material of the mid zone 115,but is rather used for its greater abrasion resistance than theelastomeric material of the mid zone 115).

To prevent excessive deformation of the drive/guide lug 48 _(i) andresultant cracking or other undesirable effects, higher modulus zonesare provided deeper inside the drive/guide lug 48 _(i) to give thedrive/guide lug 48 _(i)a more rigid skeleton. To this end, the mid zone115 and the inner zone 120 may have successively higher modulus ofelasticity values (i.e., less elasticity). The mid zone 115 may receivesome of the force transferred through the outer zone 110 and deform toabsorb part of the force transferred through the outer zone 110. Bydeforming, the mid zone 115 may absorb some of the force applied to theouter surface of the drive/guide lug 48 _(i), yet by being less elastic,the mid zone 115 strains less easily than the outer zone 110, therebyreducing the overall deformation of the drive/guide lug 48 _(i). Theinner zone 120 may have a fairly high modulus of elasticity in order tofurther rigidify the drive/guide lug 48 _(i) and prevent excessivedeformation thereof.

For instance, in some embodiments, the mid zone 115 and the inner zone120 may be made of different types of rubber such that the rubber of themid zone 115 has a lower modulus of elasticity than the rubber of theinner zone 120. The higher modulus of elasticity of the rubber of theinner zone 120 compared to that of the rubber of the mid zone 115 may beachieved in various ways, such as, for example: by having a greaterconcentration of carbon black in the rubber of the inner zone 120 thanin the rubber of the mid zone 115; by having a greater content of dienesin the rubber of the inner zone 120 than in the rubber of the mid zone115; by having a greater content of sulfur or other vulcanizing agent inthe rubber of the inner zone 120 than in the rubber of the mid zone 115;by having the rubber of the inner zone 120 and the rubber of the midzone 115 based on different base polymers; by adding a polymeric resin;and/or by using any other suitable technique.

The elastomeric material of the core zone 125 may have a highest modulusof elasticity (i.e., lowest elasticity) of the drive/guide lug 48 _(i)to serve as reinforcement to prevent deformation of the drive/guide lug48 _(i). For instance, in some cases, the elastomeric material of corezone 125 may be a rubber with a high modulus of elasticity.

In other embodiments, one or more of the outer zone 110, the mid zone115, the inner zone 120 and the core zone 125 may be made of other typesof materials, including non-elastomeric materials.

For example, in some embodiments, the outer zone 110 may be made ofthermoplastic olefin (TPO), nylon, polytetrafluoroethylene (PTFE) or anyother thermoplastic material or other material with a suitable lowcoefficient of friction and/or high abrasion resistance.

As another example, in some embodiments, the core zone 125 may be madeof metal, rigid polymer (e.g., thermoplastic), ceramic or any othermaterial with a suitable rigidity. For instance, in some cases, the corezone 125 may comprise an insert (e.g., of metal, rigid polymer orceramic) over which the rubber of the inner zone 120 is molded.

As yet another example, in some embodiments, two (2) or more of theouter zone 110, the mid zone 115, the inner zone 120 and the core zone125 may be made of a common elastomeric base in which are dispersedchopped fibers (e.g., carbon fibers, nylon fibers, Kevlar™, etc.) suchthat a concentration of the chopped fibers varies between these two ormore zones, which thereby constitute zones of different elastomericmaterials. For instance, in some cases, the outer zone 110, the mid zone115, the inner zone 120 and the core zone 125 may be made of rubbercontaining chopped Kevlar™ fibers or other suitable chopped fibers inwhich the concentration of chopped fibers decreases in the directionfrom the core zone 110 towards the outer zone 110 to reduce the modulusof elasticity in that direction.

The material distribution profile of the drive/guide lug 48 _(i)featuring the arrangement of zones 105 ₁-105 _(Z) that define themodulus of elasticity variation may thus reduce a potential for crackpropagation and thus reduce wear and increase the life of thedrive/guide lug 48 _(i).

Although a particular material distribution profile is shown in theabove embodiment for illustrative purposes to show an example of thearrangement of zones 105 ₁-105 _(Z), various other different materialdistribution profiles may be realized in other embodiments to createvarious other arrangements of zones 105 ₁-105 _(Z) by varying a numberof zones, sizes, geometries and locations of zones, and/or materials ofthe zones. For instance, while in the above embodiment there are four(4) zones of which the outer zone 110 and the mid zone 115 are layeredzones shaped like layers covering the inner zone 120 while the core zone125 is shaped like a reinforcement bar or block reinforcing thedrive/guide lug 48 _(i), in other embodiments, the number of zones andthe geometry of the zones may be varied. For example, in someembodiments, fewer zones 105 ₁-105 _(Z) may be provided to reduce thecomplexity or cost of manufacture of the drive/guide lug 48 _(i) (e.g.,core zone 125 or mid zone 115 may be omitted), or more zones 105 ₁-105_(Z) may be provided to achieve a more complex property variationprofile.

Also, although in the above embodiment the zones 105 ₁-105 _(Z) arecharacterized by certain values of modulus of elasticity, in someembodiments, other property constraints may also be taken intoconsideration in selecting the types of materials that may be used ineach zone. For example, although a high modulus of elasticity may bedesired for the inner zone 120, a certain minimum acceptable fatiguestrength may also apply in to inner zone 120 and/or in other zones.

By selecting a number of zones, sizes, geometries and locations ofzones, and/or materials of the zones, it is possible to regulate how themodulus of elasticity changes across the arrangement of zones 105 ₁-105_(Z) of the drive/guide lug 48 _(i). In the above embodiment, themodulus of elasticity varies across the drive/guide lug 48 _(i) in three(3) discrete steps, the transitions between which correspond to thetransitions between the zones 105 ₁-105 _(Z). There may be two (2), four(4), five (5) or more (e.g., 10 or 20) discrete steps in otherembodiments. By providing a large number of zones 105 ₁-105 _(Z) havingdifferent modulus of elasticity values, it is possible to approximate asmooth variation in modulus of elasticity, the actual granularity ofwhich will depend upon the number and size of the zones 105 ₁-105 _(Z).

FIGS. 11A and 11B shows other examples of embodiments of a drive/guidelug 48 _(i) in which the modulus of elasticity varies in discrete stepssuch that the zones 105 ₁-105 _(Z) have different modulus of elasticityvalues.

More particularly, FIG. 11A shows an embodiment in which the zones 105₁-105 _(Z) of the drive/guide lug 48 _(i) comprise a core zone 1115 anda plurality of layered zones, including a first layered zone 1111, asecond layered zone 1112, a third layered zone 1113 and a fourth layeredzone 1114, which make up a layered area 1120. In this example, thelayered zones 1111, 1112, 1113, 1114 are approximately equal inthickness. Different ones of the layered zones may have differentthicknesses in other examples.

FIG. 12A is a graph 1200 showing an example of how the modulus ofelasticity 1205 of the drive/guide lug 48 _(i) varies as a function ofdistance within the drive/guide lug 48 _(i) in a specified directionrepresented by line E shown in FIG. 11A, according to the embodimentillustrated in FIG. 11A. As the distance along line E is varied, themodulus of elasticity of the drive/guide lug 48 _(i) takes on five (5)different values λ₁₁₁₅, λ₁₁₁₄, λ₁₁₁₃, λ₁₁₁₂ and λ₁₁₁₁, each of whichcorrespond to the modulus of elasticity of the material of a respectiveone of the zones 1115, 1114, 1113, 1112 and 1111. As such, the functionof the modulus of elasticity 1205 of takes the form of a step function,each step corresponding to a respective one of the zones 105 ₁-105 _(Z).The layered zones 1111, 1112, 1113, 1114 are represented in range 1210of the graph 1200, while range 1215 represents the core zone 1115. Inrange 1210, the modulus of elasticity of the drive/guide lug 48 _(i)approximates a linear function 1220. As such, the layered area 1120 canbe viewed as exhibiting an approximately linear variation in modulus ofelasticity with an actual granularity defined by the steps in thefunction of the modulus of elasticity 1205 corresponding to the layeredzones 1114, 1113, 1112 and 1111. The overall function modulus ofelasticity 1205 across line E in this example can thus be considered toapproximate smooth line 1225.

In this example, the values of modulus of elasticity λ₁₁₁₅, λ₁₁₁₄,λ₁₁₁₃, λ₁₁₁₂ and λ₁₁₁₁ vary from one zone to the next by approximatelythe same value, giving steps of approximately equal height in thevertical direction of the graph 1200. Similarly, the layered zones 1111,1112, 1113, 1114 have approximately equal thicknesses such that thesteps have approximately equal width in the horizontal (distance alongline E) direction of the graph 1200. The linear function 1220 which isapproximated by the function of the modulus of elasticity 1205 in thelayered area 1120 can be varied by altering the thicknesses of thelayered zones 1111, 1112, 1113, 1114 and/or by varying the modulus ofelasticity values λ₁₁₁₅, λ₁₁₁₄, λ₁₁₁₃, λ₁₁₁₂ and λ₁₁₁₁ of the layeredzones 1111, 1112, 1113, 1114. For example, the rate of change (slope) ofthe approximated linear function 1220 may be decreased by increasing thethickness or decreasing the variation in the modulus of elasticity inthe different zones.

The manner in which approximation of a function is determined may affectthe thicknesses of the zones 105 ₁-105 _(Z) required to approximate thefunction. For example, in some embodiments, the linear function 1220 maybe arrived at by taking a weighted average of the modulus of elasticityvalues λ₁₁₁₅, λ₁₁₁₄, λ₁₁₁₃, λ₁₁₁₂ and λ₁₁₁₁ of each zone, wherein thethickness of each zone determines the weight, and dividing the result bythe average thickness of a zone. This may provide the slope of thelinear function 1220. Other models may be used in other embodiments toapproximate functions of variation of a material property depending onthe method used.

Depending on the materials available, on the modulus of elasticity ofavailable materials, and on the inter-compatibility of materials fromwhich the drive/guide lug 48 _(i) may be made, it may not practical insome embodiments to obtain equidistant moduli of elasticity for each ofthe zones 105 ₁-105 _(Z). As such, in some cases, the materials used oravailable may not provide equal heights for each step in the function ofthe modulus of elasticity 1205. In such cases, the thicknesses of thezones 105 ₁-105 _(Z) may be modified to adjust the weight of each zonesuch that, on average, the linear function 1220 is still approximated.This would have the effect of altering the horizontal length of thesteps in the graph 1200 to compensate for inequality in the verticalheight of the steps, so as to achieve an approximation of linearfunction 1220. Alternatively, the modulus of elasticity of other zonesmay be adjusted, insofar as possible or practical, such as toapproximate the linear function 1220. This would have the effect ofvarying the vertical height of steps in the graph 1200 to compensate foranother step that is too tall or too short so as to approximate thelinear function 1220.

In this embodiment, the arrangement of zones 105 ₁-105 _(Z) has beenselected based on modulus of elasticity values so as to achieve anapproximation, according to a selected curve-fitting method, of thelinear function 1220. In other embodiments, the modulus of elasticityvariation may be a nonlinear variation of a function of distance withinthe drive/guide lug 48 _(i). In yet other embodiments, there may be noapproximation of a linear or other function. For example, in someembodiments, it may simply be desired to achieve a certain modulus ofelasticity value in a central portion of the drive/guide lug 48 _(i) toprevent excessive deformation of the drive/guide lug 48 _(i) and toachieve certain other modulus of elasticity values in other areas of thedrive/guide lug 48 _(i) to allow absorption of forces applied to thedrive/guide lug 48 _(i). In such embodiments, the various materials forthe zones 105 ₁-105 _(Z) may be selected on the basis of the desiredmodulus of elasticity in each zone, without regards to any linear orother function.

FIG. 11B shows another example of an embodiment of a drive/guide lug 48_(i) in which the modulus of elasticity varies in discrete steps suchthat the zones 105 ₁-105 _(Z) have different modulus of elasticityvalues. In this embodiment, an entirety of the drive/guide lug 48 _(i)is made up of zones 105 ₁-105 _(Z) that may be considered layered zones.Also, in this embodiment, the drive/guide lug 48 _(i) comprises an innerarea 1140 where the zones 105 ₁-105 _(Z) form thicker layers 1131, 1132,1133, 1134 and an outer area 1145 where the zones 105 ₁-105 _(Z) formthinner layers 1126, 1127, 1128, 1129.

FIG. 12B shows a graph 1250 showing the function of the modulus ofelasticity 1255 of the drive/guide lug 48 _(i) as it varies along line Fshown in FIG. 11B, according to the embodiment illustrated in FIG. 11B.In this example, the modulus of elasticity decreases in successive onesof the zone 105 ₁-105 _(Z) along the line F. Also, in this example, dueto the discrete nature of the zones 105 ₁-105 _(Z), the function of themodulus of elasticity 1255 still features steps, however the steps arenot of equal size.

A first range 1240 of the graph 1250 represents the thicker layers 1131,1132, 1133, 1134 in the inner area 1140 of the drive/guide lug 48 _(i).These thicker layers 1131, 1132, 1133, 1134 do not vary equally. Inparticular, the two first thicker layers 1131 and 1132 have aparticularly high modulus of elasticity and represent a particularlyinelastic core of the drive/guide lug 48 _(i). Subsequent thicker layers1133 and 1134 have approximately the same thickness as the two firstthicker layers 1131 and 1132, but they have significantly lower moduliof elasticity. In the inner area 1140, the variation of modulus ofelasticity is not equal amongst the different zones, and the function ofthe modulus of elasticity 1255 in this first range 1240 approximates apolynomial function 1260. In this case, the materials of the thickerzones 1131, 1132, 1133, 1134 have been selected so as to achieve anapproximation, according to a selected curve-fitting method, of thepolynomial function 1260. In other cases, it may not be necessary ordesired to approximate a linear, polynomial, or other function. Forexample, the materials of the thicker zone 1131, 1132, 1133, 1134 maysimply be selected on the basis of a desired modulus of elasticity intheir respective areas.

A second range 1245 of the graph 1250 represents the thinner layers1126, 1127, 1128, 1129. These thinner layers are in the outer area 1145of the drive/guide lug 48 _(i) and provide a reduced modulus ofelasticity region for absorbing forces applied to the drive/guide lug 48_(i). While a lower modulus of elasticity may be desired towards theexterior of the drive/guide lug 48 _(i), it may be desired to avoidstrong discontinuities, that is, large differences, in the modulus ofelasticity of adjacent ones of the zones 105 ₁-105 _(Z). In particular,it may be desired to avoid having a relatively highly elastic zoneadjacent a relatively inelastic zone to avoid a stress concentration atthe interface between these zones, which could lead to cracking ortearing at the interface between these zones. In this example, strongdiscontinuities are avoided by providing four thinner layers 1126, 1127,1128, 1129 varying in modulus of elasticity from a first value λ₁₁₂₆that is near the modulus of elasticity of the adjacent thicker zone 1134gradually to a fourth value λ₁₁₂₉ at the outermost thinner zone 1129.The function of the modulus of elasticity 1255 in the second range 1245decreases as a step function with relatively equal steps whichapproximate a linear function 1265. Again, the function 1255 in thesecond range 1245 need not have equal-sized steps and may notnecessarily approximate a linear or other function.

In the above example, two areas 1140, 1145 of the drive/guide lug 48_(i) correspond to two regions 1240, 1245 of the graph approximatingdifferent functions. In other examples, a single function (linear,polynomial or other) may be approximated by the entire function of themodulus of elasticity 1255. For example, if the thicker layers 1131,1132, 1133, 1134 have an approximately corresponding step size in thefunction 1255, the thinner layers 1126, 1127, 1128, 1129 may becharacterized by variations in modulus of elasticity yielding step sizesproportional to their thinner area such that the zones 105 ₁-105 _(Z)together yield a step function that approximates a straight line.

In the embodiments considered above, the modulus of elasticity varies bydecreasing from the inside outwards. Other variations are realizable inother embodiments. For example, in some embodiments, if it is desired tohave a higher modulus of elasticity towards the outside of thedrive/guide lug 48 _(i), zones 105 ₁-105 _(Z) may similarly be providedbut with the materials in each zone having an increasing modulus ofelasticity towards the outside of the drive/guide lug 48 _(i). Asanother example, in some embodiments, successive ones of the zones 105₁-105 _(Z) from the inside to the outside of the drive/guide lug 48 _(i)may not have an ever-increasing or ever-decreasing modulus ofelasticity. Rather, the modulus of elasticity may increase and thendecrease, or vice versa, in a direction from the center of thedrive/guide lug 48 _(i) towards the outside so as to create zones havinghigher or lower modulus of elasticity values than their neighboringzones.

In some of the embodiments considered above, the zones 105 ₁-105 _(Z)are layered zones disposed on all sides of the drive/guide lug 48 _(i).In other embodiments, the layered zones may be provided only on one partof the drive/guide lug 48 _(i), such as for example only on one sidethereof. Also, in other embodiments, the zones 105 ₁-105 _(Z) may takeforms other than layers (e.g., blocks, bars or plates).

FIGS. 13A and 13B show another example of an embodiment of a drive/guidelug 48 _(i) in which the modulus of elasticity varies in discrete stepssuch that the zones 105 ₁-105 _(Z) have different modulus of elasticityvalues. In this embodiment, the drive/guide lug 48 _(i) comprises afirst zone 1300 which makes up a majority of the drive/guide lug 48 _(i)and a second zone 1305 located where a sprocket bar 52 _(i) of the drivewheel 24 contacts the drive/guide lug 48 _(i) and applies a forcethereto. The second zone 1305 may correspond roughly to the region R1shown in FIG. 8 and described above. The zone 1305 may be characterizedby a lower modulus of elasticity than the zone 1300 such that the forceapplied by the sprocket bar 52 _(i) may be better absorbed in the zone1305. Because the sprocket bar 52 _(i) is expected to contact thedrive/guide lug 48 _(i) on one side more often, the zone 1305 may beprovided only on that side of the drive/guide lug 48 _(i).Alternatively, in other cases, a zone similar to the zone 1305 may besymmetrically provided on the other side of the drive/guide lug 48 _(i).

Turning now to FIG. 13B, a third zone 1310 is provided where amid-roller 28 _(i) is expected to exert a force upon the drive/guide lug48 _(i). The zone 1310 may correspond roughly to the region R4 shown inFIG. 9 and described above. In this example, the material of the zone1310 may also extend beyond the drive/guide lug 48 _(i) into the carcass36 of the endless track 22. In particular, in this example, the materialof the zone 1310 extends into the carcass 36 of the track 22 to cover atleast part of the rolling path 33 of the inner side 45 of the track 22on which the mid-roller 28 _(i) rolls. Likewise, for layered materialdistribution profiles, such as those illustrated in FIGS. 11A and 11B,materials of certain layered zones may extend into the carcass 36 of thetrack 22.

As shown in FIG. 13B, in this case, a zone 1311 similar to the zone 1310is provided on the other side of the drive/guide lug 48 _(i) sinceconditions are expected to be symmetrically similar on both sides of thedrive/guide lug 48 _(i). Alternatively, in other cases, the zone 1310could be continuous, forming for example a circle around the peripheryof the drive/guide lug 48 _(i) or a U shape around a portion thereof.Other configurations are possible in other cases.

In embodiments considered above, the property variation profile definedby arrangement of zones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i)essentially pertains to variation of a single material property, in thiscase the modulus of elasticity. In other embodiments, the propertyvariation profile defined by the arrangement of zones 105 ₁-105 _(Z) ofthe drive/guide lug 48 _(i) may be designed such as to result in avariation of more than one property across the drive/guide lug 48 _(i).

For example, FIG. 14 shows an embodiment of a drive/guide lug 48 _(i) inwhich the arrangement of zones 105 ₁-105 _(Z) defines a propertyvariation profile that provides a variation in two properties. In thiscase, the arrangement of zones 105 ₁-105 _(Z) of the drive/guide lug 48_(i) includes zones 1405, 1411, 1412, 1413 and 1415.

The zone 1405 makes up a majority of the drive/guide lug 48 _(i), andmay have a makeup similar to that of the zone 1300 of the example ofFIGS. 13A and 13B.

The drive/guide lug 48 _(i) also comprises a certain area 1410 whereinthe material distribution profile provides a decrease in modulus ofelasticity in a direction from the center of the lug towards theperiphery of the lug. This may be realized by providing a single zonehaving a lower modulus of elasticity relative to the zone 1405 as wasprovided in the example of FIGS. 13A and 13B in the zones 1305 and 1310.However, in this example, the area 1410 is provided with the multiplezones 1411, 1412, 1413, each characterized by a different modulus ofelasticity. More particularly, in this example, the modulus ofelasticity of the zone 1411 is lower than that of the zone 1405; themodulus of elasticity of the zone 1412 is lower than that of the zone1411; and the modulus of elasticity of the zone 1413 is lower than thatof the zone 1412. As such, a layered profile with successivelydecreasing values of modulus of elasticity is achieved similarly to theexamples of FIGS. 11A and 11B, but within the area 1410. This area 1410of increased elasticity may therefore be provided where a force isexpected to be applied to the drive/guide lug 48 _(i) by the mid-roller28 _(i) such as to absorb such force. Advantageously, the reduction ofmodulus of elasticity may take place only in the area 1410 where theforce is expected to be applied. In some cases, the area 1410 may beextended in the rolling path 33 of the carcass 36 of the track 22 underthe mid-roller 28 _(i) as with the area 1310 in the example of FIG. 13B.

In order to decrease the number of different inter-zone interfaces andto avoid strong property discontinuities (e.g., as would exist at aninterface between the zone 1405 and the zone 1413, if such interfaceexisted), in this embodiment, the zone 1411 has an outward flare 1420that partially surrounds the zones 1412 and 1413 such that the zones1412 and 1413 do not extend to the zone 1405 but touch only one anotherand/or the zone 1411. The zone 1412, to a lesser extent, also has asmall flare 1421 to partially surround the zone 1413. As such, the zones1410, 1411, 1412 and 1413 only contact other zones that are one modulusof elasticity value apart.

The zone 1415 is characterized by a low coefficient of friction betweenit and the mid-roller 28 _(i). More particularly, it may be desired tohave a low coefficient of friction in the zone 1415 since, as describedabove, there may be high frictional forces between the mid-roller 28_(i) and the drive/guide lug 48 _(i). Accordingly, the zone 1415 may becharacterized as having a low friction coefficient with material whichmakes up the mid-roller 28 _(i) and which can contact the zone 1415.This material of the mid-roller 28 _(i) may be a metal (e.g., steel), alow-friction polymer (e.g., polyurethane, ultra-high-molecular-weightpolyethylene (UHMW), polytetrafluoroethylene (PTFE), etc.), or any othersuitable material. For instance, in some cases, the coefficient offriction of the zone 1415 with the material of the mid-roller 28 _(i)may be between 0.1 and 0.9. The zone 1415 may thus be made of alow-friction polymer such as polyurethane, UHMW, PTFE, etc. or any othersuitable material. Although the zone 1415 is characterized by a lowcoefficient of friction with the material of the mid-roller 28 _(i), itmay also be subject to other property constraints. For example, whilethe modulus of elasticity may be of prime concern in the area 1410,there may still be a range of acceptable modulus of elasticity for thezone 1415 as well. Other property constraints may include a minimumfatigue strength and/or a maximum hardness.

FIG. 15 shows a variation of the example of FIG. 14. Like numbered partsin FIGS. 14 and 15 represent similar elements, although the flanges 1420and 1425 have been removed in FIG. 15 for simplicity.

Like in the example of FIG. 14, in this example, the drive/guide lug 48_(i) comprises the area 1410 where the material distribution profileprovides a decrease in modulus of elasticity. This area 1410 comprisesthe zone 1413 characterized as having a certain low value modulus ofelasticity. Also, in this example, the drive/guide lug 48 _(i) comprisesa zone 1414 characterized as having the same or slightly higher value ofmodulus of elasticity as zone 1413, but also characterized as having thesame value of coefficient of friction of the zone 1415 with themid-roller 28 _(i). The properties of zone 1414 may be achieved by aparticular material that may not be the same as the material of zones1415 and 1413. For example, in some cases, TPO or polyurethane may beused in the zone 1415, a rubber may be used in the zone 1414, andanother rubber with a lower modulus of elasticity may be used in thezone 1413. A zone characterized by two desired properties may not sharevalues for those properties with adjacent zones as in the above example.For instance, the zone 1414 may be, in an alternate example,characterized by unique values of modulus of elasticity and coefficientof friction with the mid-roller 28 _(i), or may even have beencharacterized by entirely different properties.

As mentioned above, certain material properties may be dependent uponcertain physical factors and/or time. As such, when selecting a materialdistribution profile for the drive/guide lug 48 _(i) with a view ofproviding a particular property variation profile, the materialdistribution profile may comprise different materials characterized bydifferent properties wherein the difference in properties lies in thematerials' behavior at certain ranges of a physical parameter such astemperature or after a certain time. For example, in some cases, thedrive/guide lug 48 _(i) may be expected to experience a broad range oftemperatures in use (e.g., −30 to 90 degrees Celsius) and certain onesof its zones 105 ₁-105 _(Z) may be characterized by a same modulus ofelasticity at average ambient temperatures (e.g., 15-30 degrees Celsius)but have significantly different moduli of elasticity at higher or lowertemperatures as may be experienced in high stress. In such cases, aparticular zone 105 _(i) may be strategically provided to increaseresistance to wear in high stress situations. For example, if the track22 is being put to excessive use, for instance by being used inexcessively hot temperatures, for excessively high durations of time, onexcessively demanding terrain, and/or with excessive debris ingestion inthe track assembly 16 _(i), and/or by being misaligned and/or drivenexcessively hard, as the temperature increases with the ensuing highstress, the drive/guide lug 48 _(i) may have a tendency to deform more.This, in turn, may lead to premature wearing. However, if the materialdistribution profile of the drive/guide lug 48 _(i) were designedprincipally with these excessive conditions in mind, it may not beoptimally suited for use in regular conditions (e.g. it may be tooinelastic) which in turn may lead to premature wearing. One solution isto provide within the drive/guide lug 48 _(i) certain zones that arecharacterize by having certain property characteristics for physicalparameters corresponding to excessive use. For example, support zones ofmaterial having lower elasticity at high temperatures may be providedwithin the drive/guide lug 48 _(i) (e.g. as vertical strips, horizontalstrips, x-shaped reinforcement, as layers or with other geometries) toprovide support for the drive/guide lug 48 _(i) at high temperatures.

Individual ones of the discrete zones 105 ₁-105 _(Z) defining a discretegradient of modulus of elasticity, such as those considered in theembodiments discussed above, may be provided in various ways.

For example, in some embodiments, individual ones of the zones 105 ₁-105_(Z) may be separate amounts of material which are provided separatedand interconnected together. This may be done in various ways usingvarious manufacturing processes. For instance, various molding processesmay be used to make the drive/guide lug 48 _(i) with its arrangement ofzones 105 ₁-105 _(Z). For example, in some embodiments, a compressionmolding process may be used in which different pieces of material, whichare to ultimately form the zones 105 ₁-105 _(Z), may be placed in a moldsuch that, after molding, they form the arrangement of zones 105 ₁-105_(Z). As another example, in other embodiments, an injection moldingprocess may be used in which amounts of different materials which are toultimately form the zones 105 ₁-105 _(Z), may be placed in a mold suchthat, after molding, they form the arrangement of zones 105 ₁-105 _(Z).

Interconnection of the zones 105 ₁-105 _(Z) of the drive/guide lug 48_(i) may be effected in various ways.

For instance, in some embodiments, adjacent ones of the zones 105 ₁-105_(Z) may be adhesively bonded using an adhesive between them. In somecases, these zones may be created by individually molding each of themprior to gluing them together. Alternatively, in some cases, andparticularly if the zones are layered zones, the zones may be created bycutting or otherwise machining them out of a substrate prior to gluingthem together. Any suitable adhesive may be used. For instance, in somecases, various commercially-available adhesives (e.g., Chemlok™adhesives) may be used to adhesively bond adjacent different materials(e.g., rubber/metal using a Chemlok™253X adhesive, polyurethane/rubberusing a Chemlok™ 213 adhesive, polyurethane/metal using a Chemlok™ 213adhesive, etc.). In other cases, proprietary adhesives may be used.

In other embodiments, adjacent ones of the zones 105 ₁-105 _(Z) may bechemically bonded to one another. That is, a chemical bond may be formedbetween these adjacent zones during manufacturing of the drive/guide lug48 _(i). The materials of these zones may thus be bonded to one anotherwithout any adhesive. Chemical bonding between materials implies anadditional constraint to be considered when selecting the materials forthe zones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i), namely theintercompatibility of the materials. In particular, the materials usedin adjacent zones must be capable of bonding to one another under theright conditions. The conditions must then be applied to ensure thatbonding takes place. For example, in some embodiments, one type ofrubber may chemically bond with another type of rubber, UHMW maychemically bond with rubber, TPO may chemically bond with rubber, etc.

There are several ways of creating the drive/guide lug 48 _(i) withadjacent ones of the zones 105 ₁-105 _(Z) that are chemically bonded.For instance, in some embodiments, a mold having removable portionscorresponding to the various zones may be first filled with a firstmaterial, then have one or more removable portions removed, thensubsequently filled (in the resulting cavities) with a second material,and so on until every zone is filled. In other embodiments, a first moldcan be used to form a first zone 105 _(i) of the drive/guide lug 48_(i), the resulting structure being removed from the mold and laced intoanother mold for forming a second zone 105 _(i) of the drive/guide lug48 _(i) and so forth for every zone. In other embodiments, severaldifferent materials may be simultaneously injected into a given mold toform adjacent zones of the drive/guide lug 48 _(i). In yet otherembodiments, pieces of different materials, which will eventually makeup respective ones of the zones 105 ₁-105 _(Z) are prepared in advance,for instance by molding them or by cutting or otherwise machining themout of a substrate. The pieces are then arranged in their appropriateorder and relative positions, and the overall arrangement may beconsolidated, for instance by placing it in a heated mold until chemicalbonding takes place. If rubber is used, different rubber pieces, such asstrips for layered zones, may be vulcanized while together whilearranged in their proper relative positions/order, such as to form thedrive/guide lug 48 _(i) having different zones that are chemicallybonded together The pieces need not be all arranged and bonded togetherat once. For instance, if different temperatures are required to causebonding between different zones, the process may first be applied to thezones having the highest bonding temperature prior and subsequentlyapplied to zones having lower bonding temperatures.

The above-described examples of techniques may be combined together toform certain ones of the zones 105 ₁-105 _(Z) of the drive/guide lug 48_(i) using one technique and other ones of these zones using anothertechnique.

Instead of, or in addition to, being adhesively or chemically bondedtogether, in some embodiments, adjacent ones of the zones 105 ₁-105 _(Z)of the drive/guide lug 48 _(i) may be mechanically interlocked. That is,a zone 105 _(i) and a zone 105 _(i) adjacent to the zone 105 _(i) may bein a mechanical interlock relationship in which they are interconnectedvia a given one of the zone 105 _(i) and the zone 105 _(i) extendinginto the other one of the zone 105 _(i) and the zone 105 _(i). Morespecifically, a first one of the zone 105 _(i) and the zone 105 _(i)comprises an interlocking space into which extends an interlockingportion of a second one of the zone 105 _(i) and the zone 105 _(i). Theinterlocking space may comprise one or more holes, one or more recesses,and/or one or more other hollow areas. This mechanical interlockrelationship restrains movement of the zone 105 _(i) and the zone 105_(i) relative to one another. Geometric details omitted from many of theembodiments discussed above may be included in the zones 105 ₁-105 _(Z)to implement such a mechanical interlock relationship.

For example, FIG. 17A shows an embodiment in which the arrangement ofzones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i) comprise layeredzones 1705, 1710 and core zone 1715, where each of the layered zones1705, 1710 comprises an interlocking protuberance 1720, 1725 (e.g., aridge) that fits into a corresponding interlocking groove in an adjacentzone. As another example, FIG. 17B shows an embodiment in which thearrangement of zones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i)comprise a first zone 1730 and a second zone 1735, where the first zone1730 includes a fishtail interlocking portion 1740 received within acorresponding interlocking cavity in the second zone 1735. Various othermechanical interlocking arrangements are possible in other embodiments.

Adjacent ones of the zones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i)may be mechanically interlocked in various ways. For example, in somecases, adjacent ones of the zones 105 ₁-105 _(Z) of the drive/guide lug48 _(i) may be mechanically interlocked by separately creating thedifferent zones (e.g. by molding separately or cutting or otherwisemachining out of a substrate) and then assembling them together such asby snap-fitting them together. In some cases, an adhesive may be appliedprior to snap-fitting zones together. As another example, in some cases,adjacent ones of the zones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i)may be mechanically interlocked by being overmolded. Using mechanicalinterlocking, it is not necessarily required for the zones to chemicallybond. As such, overmolding may take place using incompatible materials,that is, materials not susceptible to form chemical bonds togetherduring the overmodling process, or using temperatures or orders ofmolding not susceptible to cause chemical bonding between the zones. Insome cases, it may be desired to have both chemical bonding andmechanical interlock for increased robustness. In such a case themanners of assembling the zones together may include the methods offorming chemical bonds described above.

While the above embodiments illustrate examples of making andinterconnecting the zones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i)to create the arrangement of zones 105 ₁-105 _(Z) and the desiredproperty variation profile, various other techniques may be used inother embodiments to provide the zones 105 ₁-105 _(Z) of the drive/guidelug 48 _(i). For instance, in some embodiments, a zone 105 _(i) may be acoated zone provided by painting, depositing, spattering or spraying acoating over another zone 105 _(j). The coating may be a coating ofpolyurethane, acrylic, or any other suitable material, and may have athickness of about 1 to 1.5 mil (thousandth(s) of an inch) or any othersuitable value.

Also, any suitable combination of the above techniques for creating thezones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i) may be used. Forexample, in some embodiments, individual zones on the interior of thedrive/guide lug 48 _(i) may be overmolded (e.g., with chemical bondingand/or mechanical interlocking), while an outer protective layer (e.g.,a skin or a cap) can be applied overtop the drive/guide lug 48 _(i) andheld thereon by adhesive bonding or by mechanical interlocking.Alternatively, a spray-on layer may be provided instead of oradditionally to, the protective layer as an outermost layer.

ii. Continuous Gradient

In some embodiments, the property variation profile defined by thearrangement of zones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i) mayinclude a continuous gradient of modulus of elasticity. A continuousgradient of modulus of elasticity is a continuous variation of themodulus of elasticity in a specified direction across the arrangement ofzones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i). In suchembodiments, adjacent ones of the zones 105 ₁-105 _(Z) which define thecontinuous gradient of modulus of elasticity are infinitesimal zones. Azone is “infinitesimal” in that it is sufficiently small and has asufficiently small difference in modulus of elasticity with an adjacentzone that its dimension along the specified direction of the continuousgradient is not macroscopically measurable.

For example, FIG. 18A illustrates an example of an embodiment in whichthe variation of the modulus of elasticity across the arrangement ofzones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i) includes acontinuous gradient of modulus of elasticity. In this embodiment, thecontinuous gradient extends throughout the drive/guide lug 48 _(i). FIG.18B illustrates a graph of the variation of the modulus of elasticity asa function of distance along line G shown in FIG. 18A. In this example,the spatial variation of the modulus of elasticity is a generally linearfunction 1810. Although the linear function 1810 is shown as perfectlystraight, actual realizations of the continuous gradient of modulus ofelasticity in some embodiments may not be perfect and imperfections mayresult in the variation not being perfectly linear.

In FIG. 18A, certain zones 1805 ₁-1805 _(M) of the arrangement of zones105 ₁-105 _(Z) defining the continuous gradient of modulus of elasticityare represented. The zones 1805 ₁-1805 _(M) are represented as isolines,where each isoline links points at which the value of the modulus ofelasticity is the same. The space between adjacent zones 1805 ₁, 1805 ₁includes other ones of the infinitesimal zones 105 ₁-105 _(Z) definingthe continuous gradient of modulus of elasticity.

A continuous gradient of modulus of elasticity may be configured invarious other ways in other embodiments. For example, although in theabove embodiment it is a linear function, the spatial variation of themodulus of elasticity defining the continuous gradient may be a morecomplex function (e.g., a polynomial function) in other embodiments. Asanother example, while in the above embodiment it extends throughout theentire drive/guide lug 48 _(i), the continuous gradient of modulus ofelasticity may only exist in a limited area of the drive/guide lug 48_(i) (e.g., less than half of its front-to-back or side-to-sidedimension).

Individual ones of the infinitesimal zones 105 ₁-105 _(Z) defining acontinuous gradient of modulus of elasticity, such as those consideredin the embodiments discussed above, may be provided in various ways.

For example, in some embodiments, the value of the modulus of elasticitymay be related to a mixture of two or more constituents which make upmaterial of the drive/guide lug 48 _(i). For instance the relativeconcentration of each of the constituents may determine the modulus ofelasticity of the resulting material. In such a case, any suitablefabrication method that permits gradual variation in the relativeconcentration of each of the constituents may be used to produce acontinuous gradient of modulus of elasticity.

As an example, in some embodiments, a twin injection molding techniquemay be used whereby two ingredients are injected into a mold. Therelative intensity of the two jets of ingredients may be varied as themold fills. Alternatively, rather than to vary the intensity of jetsinjecting the ingredients into the mold, the two jets may be located atdifferent locations of the mold, and the ingredients may be injected inliquefied form into the mold such that they mix between the two jets andform the drive/guide lug 48 _(i) having a gradual change in relativeconcentration of the two ingredients varying for almost uniquely a firstingredient near a corresponding first jet location to almost uniquely asecond ingredient near a corresponding second jet. As another example,in some embodiments, the drive/guide lug 48 _(i) may be made by takingtwo or more solid pieces, each made of one of two ingredients, andplacing them in relative position and heating them until they melt andmix at their interface.

While the above examples describe the use of two ingredients to achievea continuous gradient of modulus of elasticity, it should be understoodthat three or more ingredients may be used as well, wherein the relativeconcentration of the three or more ingredients determines the value of aproperty such as the modulus of elasticity modulus. In some cases, notall ingredients need to be present throughout the drive/guide lug 48_(i), since one ingredient may have a concentration of 0% in some area.As such, in a three-or-more-ingredient scheme, there may be a variationof the relative concentration of two ingredients, followed by avariation of the relative concentration of two other ingredients(including, or not, a common ingredient with the first variation). Anyother schemes for combining ingredients in varying relativeconcentration may be used to achieve a desired variation in a propertysuch as modulus of elasticity.

As another example, in some embodiments, two or more zones of thearrangement of zones 105 ₁-105 _(Z) may be formed by subjecting a commonbase material to a treatment causing at least two areas of the commonbase material to become different from one another, thus constitutingtwo zones of different materials.

For instance, in some embodiments, a continuous gradient of modulus ofelasticity may be achieved by a controlled heat treatment. For example,in some cases, an injection molding process may be used in which arubber to make the drive/guide lug 48 _(i) is injected into a mold at ahigh temperature and, as the molding process progresses, the temperaturemay be reduced to cause a smooth variation in the modulus of elasticity.Other heat treatments may be used in other cases.

As another example, in some embodiments, a continuous gradient ofmodulus of elasticity may be achieved by providing a drive/guide lug 48_(i) made of a single base material which is altered by applying apenetrating treatment such that the alteration induces a smooth changein the modulus of elasticity. For instance, in some cases, a materialfrom which to make the drive/guide lug 48 _(i) may be radiated with acertain penetrating (e.g. UV) radiation that causes a change in thematerial characteristics and that diminishes in intensity with depth. Inother cases, an additive or impurity may be added to a material fromwhich to make the drive/guide lug 48 _(i) from the outside in. Thus, theadditive or impurity may penetrate the material to a certain depthdropping in intensity as the depth is increased. This method can becombined with another penetrating treatment, such as heat application.For example, by applying sulfur (or a peroxide, or a urethanecrosslinker, or a metal oxide), or another additive to the exterior of amaterial from which to make the drive/guide lug 48 _(i) and applyingheat thereto as well, the body may be made to have different levels ofvulcanization at different depths, resulting in a variation of one ormore properties with depth.

While a penetrating treatment may be applied to a single material, insome cases, multiple materials may be subjected to the penetratingtreatment. For example, different materials having different sensitivityto the penetrating treatment may be provided at different depths tomodify the effective area over which the penetrating treatment iseffective and/or to alter the effect of the penetrating treatment.Alternatively or additionally, materials having a different reaction tothe penetrating treatment may be placed in different locations withinthe drive/guide lug 48 _(i) so as to provide areas characterized bydifferent gradients of a same or a different property.

As another example, in some embodiments, a continuous gradient ofmodulus of elasticity may be achieved by providing a large number ofthin layers each of which differs from its neighbors by a small changein modulus of elasticity. This may result in a step function with a veryfine granularity resembling a smooth function. By heating the thinlayers, certain effects may take place at the layers' interfaces whichmay cause a smoothing of the step function. For instance, in some cases,when heated to a certain temperature (e.g., at or near a melting pointof a material making up a layer), adjacent layers may intermix at theirinterface which may cause a smoothing of the step function of propertyvariation, material from one layer may diffuse into that of anotherlayer, and/or material from one layer may from cross-links with that ofanother layer.

iii. Discrete Gradient and Continuous Gradient

In some embodiments, the property variation profile defined byarrangement of zones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i) mayinclude at least one discrete gradient of modulus of elasticity and atleast one continuous gradient of modulus of elasticity. Certain ones ofthe zones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i) may be discretezones that define a discrete gradient, while other ones of the zones 105₁-105 _(Z) may be infinitesimal zones 105 ₁-105 _(Z) that define acontinuous gradient.

For instance, FIG. 19 illustrates an example of such an embodiment,which is similar to the example of FIG. 14, but with the area 1410 whichcomprises three discrete zones 1411, 1412, 1413 in the example of FIG.14 replaced by an area 1905 comprising infinitesimal zones defining acontinuous gradient of modulus of elasticity wherein the modulus ofelasticity decreases along line H.

Various other combinations of discrete gradients and continuousgradients are possible in other embodiments (e.g., an outer spray-on orsheet layer with a continuous gradient in a remainder of the drive/guidelug 48 _(i)).

iv. Property Variation Characterization

The property variation profile defined by arrangement of zones 105 ₁-105_(Z) of a drive/guide lug 48 _(i) may be characterized in various ways.

For example, a ratio λ_(i)/λ_(j) of the modulus of elasticity λ_(i) of azone 105 _(i) and the modulus of elasticity λ_(j) of a zone 105 _(j)adjacent to the zone 105 ₁, where Δ_(j)>Δ_(i) such that 0<λ_(i)/λ_(j)<1,may take on various values. For instance, in some embodiments, the ratioλ_(i)/λ_(j) may be at least 0.2, in some cases at least 0.3, in somecases at least 0.4, in some cases at least 0.5, in some cases at least0.6, in some cases at least 0.7, in some cases at least 0.8, in somecases at least 0.9, and even more in some cases (e.g., 0.95 or more).Values of the ratio λ_(i)/λ_(j) closer to one, such as for instancebetween 0.6 and 1 or particularly between 0.7 and 1, may be desired insome cases. This may avoid too great of a difference in modulus ofelasticity between the adjacent zones 105 _(i), 105 _(j) which couldcreate a stress concentration at the interface between these zones,which could lead to cracking or tearing at the interface between thesezones.

As another example, a ratio λ_(min)/λ_(max) of the minimum modulus ofelasticity λ_(min) of the drive/guide lug 48 _(i) and the maximummodulus of elasticity λ_(max) of the drive/guide lug 48 _(i) may take onvarious values. For instance, in some embodiments, the ratioλ_(min)/λ_(max) may be at least 0.2, in some cases at least 0.3, in somecases at least 0.4, in some cases at least 0.5, in some cases at least0.6, in some cases at least 0.7, in some cases at least 0.8, in somecases at least 0.9, and even more in some cases (e.g., 0.95 or more).

As another example, a gradient of the modulus of elasticity of thedrive/guide lug 48 _(i) has a spatial rate of changeΔλ/D=(λ_(high)−λ_(low))/D, where Δλ=(λ_(high)−λ_(low)) is an increase inthe modulus of elasticity between a point P_(low) with the modulus ofelasticity λ_(low) and a point P_(high) with the modulus of elasticityλ_(high), which may take on various values. In embodiments in whichindividual ones of the zones 105 ₁-105 _(Z) that define the gradient arediscrete such that the gradient is a discrete gradient, the spatial rateof change Δλ/D can be evaluated by taking the points P_(low) andP_(high) as midpoints of those zones which respectively have the moduliiof elasticity how and λ_(high). For instance, in some embodiments, thespatial rate of change Δλ/D may be no more 5 MPa/mm, in some cases nomore than 4 MPa/mm, in some cases no more than 3 MPa/mm, in some casesno more than 2 MPa/mm, and in some cases no more than 1 MPa/mm. This mayavoid too great of a difference in modulus of elasticity between thezones which could create a stress concentration at the interface betweenthese zones, which could lead to cracking or tearing at the interfacebetween these zones.

As another example, in some embodiments, a size of one or more of thezones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i) may be considered.For instance, in some cases, a first one of the zones 105 ₁-105 _(Z)that is more inward than a second one of the zones 105 ₁-105 _(Z) may bethicker than the second one of the zones 105 ₁-105 _(Z). For instance,an example of such an embodiment is shown in FIGS. 10A and 10B where theeach of the inner zone 120 and the core zone 125 is thicker than theouter zone 110 or the mid zone 115. In some examples, an innermost oneof the zones 105 ₁-105 _(Z) may be a thickest one of the zones 105 ₁-105_(Z).

As yet another example, in some embodiments, a size and elasticity ofone or more of the zones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i)may be considered together. For instance, in some cases, a first one ofthe zones 105 ₁-105 _(Z) that is thicker than a second one of the zones105 ₁-105 _(Z) may be stiffer than the second one of the zones 105 ₁-105_(Z). For instance, an example of such an embodiment is shown in FIGS.10A and 10B where the core zone 125 is thicker and stiffer than theouter zone 110. In some examples, a thickest one of the zones 105 ₁-105_(Z) may be a stiffer one of the zones 105 ₁-105 _(Z).

Although in embodiments discussed above the property variation profiledefined by the arrangement of zones 105 ₁-105 _(Z) includes a variationof the modulus of elasticity across the drive/guide lug 48 _(i), inother embodiments, the property variation profile may include avariation of one or more other material properties in addition to orinstead of a variation of the modulus of elasticity.

For example, in some embodiments, the property variation profile mayinclude a variation of a tensile strength across the arrangement ofzones 105 ₁-105 _(Z). For instance, in some cases, the variation of thetensile strength may include an increase of the tensile strengthinwardly such that a zone 105 _(i) is more inward and has a greatertensile strength than a zone 105 _(i) (e.g., the zone 105 _(i) may be anoutermost elastomeric zone and the zone 105 _(j) may be an underlyingelastomeric zone). In other cases, the variation of the tensile strengthmay include an increase of the tensile strength outwardly such that azone 105 _(j) is more outward and has a greater tensile strength than azone 105 _(i) (e.g., the zone 105 _(j) may be an outermost elastomericzone and the zone 105 _(i) may be an underlying elastomeric zone).

As another example, in some embodiments, the property variation profilemay include a variation of a crack propagation resistance across thearrangement of zones 105 ₁-105 _(Z). The crack propagation resistance ofa zone 105 _(x), which can also be referred to a crack growthresistance, refers to a resistance of material making up the zone 105_(x) to crack propagation. For example, the crack propagation resistanceof the zone 105 _(x) can be evaluated on a basis of a crack growth rate(e.g., in mm per number of cycles) measured using a suitable crackgrowth test (e.g., a pure-shear crack growth test) on the materialmaking up the zone 105 _(x), such that the crack propagation resistanceis inversely related to the crack growth rate (i.e., the lower the crackgrowth rate, the higher the crack propagation resistance). For instance,in some cases, the variation of the crack propagation resistance mayinclude an increase of the crack propagation resistance outwardly suchthat a zone 105 _(i) is more outward and has a greater crack propagationresistance (i.e., a lower crack growth rate) than a zone 105 _(i) (e.g.,the zone 105 _(j) may be an outermost elastomeric zone and the zone 105_(i) may be an underlying elastomeric zone). In other cases, thevariation of the crack propagation resistance may include an increase ofthe crack propagation resistance inwardly such that a zone 105 _(i) ismore inward and has a greater crack propagation resistance (i.e., alower crack growth rate) than a zone 105 _(i) (e.g., the zone 105 _(i)may be an outermost elastomeric zone and the zone 105 _(j) may be anunderlying elastomeric zone).

Principles discussed above in respect of the variation of modulus ofelasticity may therefore also apply to a variation of another materialproperty. For instance, the examples of property variationcharacterization discussed above in respect of the modulus of elasticityλ can be expressed in terms of any desired material property P.

b) Zone with Dedicated Function

In some embodiments, one or more of the zones 105 ₁-105 _(Z) of thedrive/guide lug 48 _(i) may be provided to implement a dedicatedfunction. Examples of such dedicated functions are discussed below.

i. Wear Indicator Zone

In some embodiments, one or more zones of the arrangement of zones 105₁-105 _(Z) of a drive/guide lug 48 _(i) may implement a wear indicatorto indicate a level of wear of the drive/guide lug 48 _(i).

FIG. 16 illustrates an example in which the arrangement of zones 105₁-105 _(Z) includes several layered zones 1610 ₁-1610 ₄ characterized bya variation in modulus of elasticity which may be varied similarly towhat was described in the example of FIG. 11A. In this example, thedrive/guide lug 48 _(i) also includes a colored zone 1605, which besidesbeing characterized by having a particular modulus of elasticity, isalso characterized by having a distinctive color. The layer 1605 havinga distinctive color may be useful in allowing visual determination of alevel of wear of the drive/guide lug 48 _(i). When through prolongeduse, the outer layers 1615 ₁, 1615 ₂ wear out, at least in some areas,the colored zone 1605 becomes exposed making it possible to see, fromthe color, that the wear of the drive/guide lug 48 _(i) has reached thelevel of colored zone 1605. This may be useful as an indicator that itis time to service or replace the drive/guide lug 48 _(i) or the track22 altogether. Exposure of the colored zone 1605 may also indicate thatthe drive/guide lug 48 _(i) has shed its two outermost layers 1615 ₁,1615 ₂ and now has a modulus of elasticity on its exterior that isoutside of an operationally acceptable range for the track 22.

In other embodiments, the colored zone 1605 may be characterized by itscolor only and not its modulus of elasticity. Also, in otherembodiments, a colored zone such as the colored zone 1605 may extendinto the carcass 36 of the track 22 (e.g., in the rolling path 33) suchas to provide visual indication of wear in the carcass 36 of the track22 as well.

FIG. 20 illustrates another example of an embodiment in which a zoneimplements a wear indicator. In this embodiment, the arrangement ofzones 105 ₁-105 _(Z) of the drive/guide lug 48 _(i) comprisesinfinitesimal zones that define a continuous gradient of modulus ofelasticity along line I, in a manner similar to that discussed above inrespect of FIG. 18A. In this example, the drive/guide lug 48 _(i) alsocomprises a zone 2005 characterized by having a certain color thatserves as a wear marker.

A wear indicator zone may be configured in various other ways in otherembodiments.

ii. Sacrificial Zone

In some embodiments, a zone 105 _(i) of the drive/guide lug 48 _(i) maybe a sacrificial zone that is intended to be sacrificed during use ofthe endless track 22. For instance, the sacrificial zone may be intendedto protect the lug during a break-in period. The sacrificial zone maydisappear by wearing out through abrasion, by undergoing a phasetransition (e.g., liquefaction, evaporation or sublimation) due totemperature and/or pressure, and/or by experiencing any other processoccurring during use of the track 22. For example, in some cases, thesacrificial zone may be a protective layer or coating at the outermostpart of the drive/guide lug 48 _(i) that is provided to the drive/guidelug 48 _(i) (e.g. by molding, adhesive bonding, mechanical interlocking,painting-on, spraying-on, etc.) that is intended to wear off in acertain amount of time and/or when reaching a certain temperature.Various soft materials may be used for the protective layer or coating(e.g., wax, silicone, PTFE-based, etc.). For instance, in someembodiments, the sacrificial zone may be a PTFE-based coating or otherlow-friction coating that wears off with time.

iii. State-Changing Zone

In some embodiments, a zone 105 _(i) of the drive/guide lug 48 _(i) maybe a state-changing zone that undergoes a change in state during use ofthe track 22. For example, a particular material may harden with time,while another may undergo a permanent change in modulus of elasticitywhen a certain temperature is reached, etc. For instance, in some cases,such changes may be planned and anticipated as part of a break-in periodof the endless track 22. The material distribution profile of thedrive/guide lug 48 _(i) may be designed in such a manner as to yield adesired property variation profile after the break-in period, but mayhave less-than-ideal properties before and during the break-in period.In other cases, the changes may be planned for when the track 22 is usedafter its break-in period.

Although various examples of a drive/guide lug 48 _(i) with a materialdistribution profile have been considered above, a drive/guide lug 48_(i) may have various other material distribution profiles in otherembodiments.

2. Drive/Guide Lug with a Particular Shape

In some embodiments, a drive/guide lug 48 _(i) may have a particularshape to enhance its wear resistance or otherwise enhance itsperformance.

a) Drive Lug with Uneven Drive Surface

In some embodiments in which the drive wheel 24 is a sprocket, as shownin FIG. 21, the drive surface 80 ₁ of a drive/guide lug 48 _(i) may beuneven (i.e., non-flat) such that an uneven portion 82 of thedrive/guide lug 48 _(i) contacts a drive member 52 _(i) of the sprocket24 when the drive/guide lug 48 _(i) engages the drive member 52 _(i).For example, in this embodiment, the drive surface 80 ₁ of thedrive/guide lug 48 _(i) may be in generally conformity with a drivesurface 68 ₁ of the drive member 52 _(i) of the sprocket 24. Thisincreases a contact area of the drive/guide lug 48 _(i) which contactsthe drive member 52 _(i) of the sprocket 24 in order to enhance loaddistribution on the drive/guide lug 48 _(i) and on the drive member 52_(i) of the sprocket 24. The contact area of the drive/guide lug 48 _(i)is increased in that it is greater than if the drive surface 80 ₁ of thedrive/guide lug 48 _(i) was substantially flat but the drive/guide lug48 _(i) was otherwise identical. By distributing the load over a greatercontact area, stress on the drive/guide lug 48 _(i) is reduced.

In this embodiment, the uneven portion 82 of the drive/guide lug 48 _(i)is a protrusion extending towards the drive member 52 _(i) of thesprocket 24 when the drive/guide lug 48 _(i) engages the drive member 52_(i). The protrusion 82 protrudes towards the drive member 52 _(i) ofthe sprocket 24 beyond an imaginary flat plane FS extending where thedrive surface 80 ₁ of the drive/guide lug 48 _(i) would be if it wasflat. The drive surface 80 ₁ of the drive/guide lug 48 _(i) is uneven inthe widthwise direction of the endless track 22 to form the protrusion82. The drive/guide lug 48 _(i) thus tapers in the widthwise directionof the track 22.

Also, in this embodiment, the drive surface 68 ₁ of the drive member 52_(i) of the sprocket 24 is uneven and forms a recess 83 of the drivemember 52 _(i). The protrusion 82 of the drive/guide lug 48 _(i) extendsinto the recess 83 of the drive member 52 _(i) when the drive/guide lug48 _(i) engages the drive member 52 _(i). In some cases, the protrusion82 of the drive/guide lug 48 _(i) may extend into the recess 83 of thedrive member 52 _(i) such that an apex 84 of the protrusion 82 contactsthe drive member 52 _(i). In other cases, the protrusion 82 of thedrive/guide lug 48 _(i) may extend into the recess 83 of the drivemember 52 _(i) such that the apex 84 of the protrusion 82 does notcontact the drive member 52 _(i).

More particularly, in this embodiment, the drive surface 80 ₁ of thedrive/guide lug 48 _(i) is angled in that it defines an oblique angle β′relative to the widthwise direction of the endless track 22. Forinstance, in some embodiments, the angle β′ may be at least 0.25°, insome cases at least 0.5°, in some cases at least 0.75°, in some cases atleast 1°, in some cases at least 1.25°, in some cases at least 1.5°, insome cases at least 1.75°, in some cases at least 2°, in some cases atleast 3°, in some cases at least 5°, and in some cases even more (e.g.,at least 10° or 15°). The angle β′ may take on any other suitable valuein other embodiments.

Also, in this embodiment, the drive surface 68 ₁ of the drive member 52_(i) of the sprocket 24 is angled in that it defines an oblique angle βrelative to a direction parallel to an axis of rotation of the sprocket24. In this case, the angle β is a draft angle used during manufacturingof the sprocket 24 to facilitate a casting process used to make thesprocket 24. For instance, in some embodiments, the angle β may be atleast 0.25°, in some cases at least 0.5°, in some cases at least 0.75°,in some cases at least 1°, in some cases at least 1.25°, in some casesat least 1.5°, in some cases at least 1.75°, in some cases at least 2°,or even more in some cases. The angle β′ defined by the drive surface 80₁ of the drive/guide lug 48 _(i) is thus selected to accommodate theangle β defined by the drive surface 68 ₁ of the drive member 52 _(i).For instance, in some embodiments, a ratio β′/β of the angle β′ of thedrive surface 80 ₁ of the drive/guide lug 48 _(i) and the angle β of thedrive surface 68 ₁ of the drive member 52 _(i) may be between 0.5 and1.5, in some cases between 0.7 and 1.4, in some cases between 0.8 and1.2, in some cases between 0.9 and 1.1, and in some cases 1.0.

The drive surface 80 ₁ of the drive/guide lug 48 _(i) and the drivesurface 68 ₁ of the drive member 52 _(i) may have various other unevenforms that are in general conformity with one another in otherembodiments. For example, in some embodiments, instead of just oneoblique angle as in the embodiment considered above, each of the drivesurface 80 ₁ of the drive/guide lug 48 _(i) and the drive surface 68 ₁of the drive member 52 _(i) may have two (2) or more similar obliqueangles. As another example, in some embodiments, instead of or inaddition to being angled, each of the drive surface 80 ₁ of thedrive/guide lug 48 _(i) and the drive surface 68 ₁ of the drive member52 _(i) may be curved in such a way that their respective curvatures arein generally conformity to one another.

The drive surface 80 ₁ of the drive/guide lug 48 _(i) and thus theuneven portion 82 of the drive/guide lug 48 _(i) may have various otheruneven forms in other embodiments. For example, instead of being aprotrusion, in other embodiments, the uneven portion 82 of thedrive/guide lug 48 _(i) may be a recess facing the drive member 52 _(i)of the sprocket 24 when the drive/guide lug 48 _(i) engages the drivemember 52 _(i). As another example, in other embodiments, instead of orin addition to being angled, the drive surface 80 ₁ of the drive/guidelug 48 _(i) and thus the uneven portion 82 of the drive/guide lug 48_(i) may be curved (e.g., convexly and/or concavely curved). FIG. 22shows an example of an embodiment in which the drive surface 80 ₁ of thedrive/guide lug 48 _(i) and thus the uneven portion 82 of thedrive/guide lug 48 _(i) are curved.

In this embodiment, a description similar to that presented above inrespect of the drive surface 80 ₁ of the drive/guide lug 48 _(i) and thedrive surface 68 ₁ of the drive member 52 _(i) applies to the drivesurface 80 ₂ of the drive/guide lug 48 _(i) and a drive surface 682 ofthe drive member 52 _(i) of the sprocket 24. In other embodiments, onlyone of the drive surfaces 80 ₁, 80 ₂ of the drive/guide lug 48 _(i) maybe uneven as described above while the other one may be substantiallyflat.

Although in this embodiment the uneven portion 82 of the drive/guide lug48 _(i) is an integral portion of the drive/guide lug 48 _(i) (e.g.,molded elastomeric material of the drive/guide lug 48 _(i)), in otherembodiments, the uneven portion 82 of the drive/guide lug 48 _(i) may beformed by a removable member of the drive/guide lug 48 _(i) that ismounted to a core of the drive/guide lug 48 _(i) and that has an unevenouter surface providing the uneven drive surface 80 ₁ of the drive/guidelug 48 _(i). For example, in some embodiments, the removable member maycomprise a cap that is mounted to the core of the drive/guide lug 48_(i). The core of the drive/guide lug 48 _(i) may have a generally flatsurface facing towards the drive member 52 _(i) of the sprocket 24 whenthe drive/guide lug 48 _(i) engages the drive member 52 _(i). Theremovable member may have a generally flat inner surface facing thegenerally flat surface of the core of the drive/guide lug 48 _(i), whilethe removable member's uneven outer surface provides the uneven drivesurface 80 ₁ of the drive/guide lug 48 _(i). For instance, in suchembodiments, what is shown in FIGS. 21 and 22 would be the removablemember, with the core of the drive/guide lug 48 _(i) being locatedunderneath the removable member.

While in this embodiment the drive surface 68 ₁ of the drive member 52_(i) of the sprocket 24 is uneven, in other embodiments, the drive/guidelug 48 _(i) with its uneven portion 82 may be used in cases where thedrive surface 68 ₁ of the drive member 52 _(i) is substantially flat.

b) Drive/Guide Lug Avoiding Interference with Mid-Roller Support

In some embodiments in which a drive/guide lug 48 _(i) is used to guidethe endless track 22 by passing between laterally adjacent ones of themid-rollers 28 ₁-28 ₆, the drive/guide lug 48 _(i) may be configured toreduce a potential for interference with a mid-roller support 70 whichcarries one or more of the mid-rollers 28 ₁-28 ₆, includes the axle 94of each of these one or more carried mid-rollers, and is located abovethe drive/guide lug 48 _(i), as shown in FIG. 23. In this example, themid-roller support 70 includes the axle 94 which is a common axle of themid-rollers 28 _(i), 28 _(j). Also, in this example, the mid-rollersupport 70 is pivotable relative to the frame 13 of the track assembly16 _(i) about a pivot axis 62 (e.g., such as a pivot axis 71 ₁ or 71 ₂shown in FIG. 1) to allow the mid-rollers 28 _(i), 28 _(j) to move upand down relative to the frame 13 of the track assembly 16 _(i). Themid-roller support 70 may be configured in various other ways in otherexamples. For instance, in other examples, a mid-roller carried by themid-roller support 70 may have its own dedicated axle 94 and/or themid-roller support 70 may not be pivotable relative to the frame 13 ofthe track assembly 16 _(i).

Certain factors can be taken into account to reduce the potential forinterference between the drive/guide lug 48 _(i) and the mid-rollersupport 70. For example, in some cases:

-   -   The mid-rollers 28 _(i), 28 _(j) may reduce in diameter as they        wear out. For instance, in some embodiments, each of the        mid-rollers 28 _(i), 28 _(j) may comprise a rubber or other        elastomeric covering 73 on its circumference to enhance friction        with the rolling path 33 of the inner side 45 of the endless        track 22.

Such a covering 73 is represented in dotted line in FIG. 23. As thisrubber or other elastomeric covering 73 wears off during use, thediameter of each of the mid-rollers 28 _(i), 28 _(j) is reduced,bringing the mid-roller support 70 down closer to the drive/guide lug 48_(i). In other embodiments, no such covering 73 may be provided but themid-rollers 28 _(i), 28 _(j) may nevertheless reduce in diameter as theymaterial wears off.

-   -   The tread pattern 40 and its traction lugs 58 ₁-58 _(T) may wear        unevenly in the widthwise direction of the endless track 22 such        that the tread pattern 40 is thinner in one half of the width of        the endless track 22. This causes the drive/guide lug 48 _(i) to        be inclined relative to the horizontal and thus the mid-roller        support 70 to be closer to a top corner region of the        drive/guide lug 48 _(i).    -   The endless track 22 may be misaligned in the widthwise        direction of the track assembly 16 _(i).    -   The tension in the endless track 22 may be low (e.g, causing        deformation or deflection in the center of the track 22).

The drive/guide lug 48 _(i) may be configured such that, when theendless track 22 is new and the mid-rollers 28 _(i), 28 _(j) are new, avertical clearance V between the drive/guide lug 48 _(i) and themid-roller support 70 is sufficient to avoid interference between thedrive/guide lug 48 _(i) and the mid-roller support 70 as the trackassembly 16 _(i) is used. The vertical clearance V may take one variousvalues in various embodiments. For example, in some embodiments, thevertical clearance V may be at least 6 mm (e.g., in cases where nocovering 73 is provided on the mid-rollers 28 _(i). 28 _(j)), in somecases at least 9 mm, in some cases at least 12 mm, in some cases atleast 15 mm, in some cases at least 18 mm, in some cases at least 21 mm,or even more in some cases.

As shown in FIG. 23, in some embodiments, the drive/guide lug 48 _(i)may be shaped to provide for the vertical clearance V and thus reducethe potential for interference with the mid-roller support 70.

For example, in some cases, the drive/guide lug 48 _(i) may be shapedsuch that, when the diameter of each of the mid-rollers 28 ₁-28 ₆ hasreduced to its minimum during normal use, the drive/guide lug 48 _(i)clears the mid-roller support 70 without interference. For instance, inembodiments in which each of the mid-rollers 28 _(i), 28 _(j) comprisesa rubber or other elastomeric covering 73 on its circumference, a heightH of the drive/guide lug 48 _(i) may be sufficiently small that, whenthe covering 73 has worn off, i.e., the diameter of each of themid-rollers 28 ₁-28 ₆ has reduced by an amount corresponding to anoriginal thickness T of the covering 73, the drive/guide lug 48 _(i)clears the mid-roller support 70 without interference.

Embodiments discussed above thus provide solutions to enhance the wearresistance and/or otherwise enhance the performance of the drive/guidelugs 48 ₁-48 _(N) of the endless track 22. While these solutions werediscussed separately, in some embodiments, any feature of any embodimentdescribed herein may be used in combination with any feature of anyother embodiment described herein.

Although potentially less severe than wear or other deterioration of thedrive/guide lugs 48 ₁-48 _(N) of the endless track 22, in some cases,wear or other deterioration of the traction lugs 58 ₁-58 _(T) (e.g., dueto particularly abrasive ground material) can sometimes becomesignificant enough to adversely affect performance or appearance of theendless track 22. Thus, in some embodiments, solutions described abovein respect of the drive/guide lugs 48 ₁-48 _(N) may be similarly appliedto the traction lugs 58 ₁-58 _(T).

Each track assembly 16 _(i) of the agricultural vehicle 10, includingits endless track 22, may be configured in various other ways in otherembodiments.

For example, each track assembly 16 _(i) may comprise different and/oradditional components in other embodiments. For example, in someembodiments, the track assembly 16 _(i) may comprise a front drive wheel(e.g., the idler wheel 26 may be replaced by a drive wheel) instead ofor in addition to the drive wheel 24. As another example, in someembodiments, the track assembly 16 _(i) may comprise more or less rollerwheels such as the roller wheels 28 ₁-28 ₆. As yet another example,rather than have a generally linear configuration as in this embodiment,in other embodiments, the track assembly 16 _(i) may have various otherconfigurations (e.g., a generally triangular configuration with the axisof rotation of the drive wheel 24 located between the axes of rotationsof leading and trailing idler wheels).

While in the embodiment considered above the off-road vehicle 10 is anagricultural vehicle, in other embodiments, the vehicle 10 may be anindustrial vehicle such as a construction vehicle (e.g., a loader, abulldozer, an excavator, etc.) for performing construction work or aforestry vehicle (e.g., a feller-buncher, a tree chipper, a knuckleboomloader, etc.) for performing forestry work, or a military vehicle (e.g.,a combat engineering vehicle (CEV), etc.) for performing military work,or any other vehicle operable off paved roads. Although operable offpaved roads, the vehicle 10 may also be operable on paved roads in somecases. Also, while in the embodiment considered above the vehicle 10 isdriven by a human operator in the vehicle 10, in other embodiments, thevehicle 10 may be an unmanned ground vehicle (e.g., a teleoperated orautonomous unmanned ground vehicle).

Although various embodiments and examples have been presented, this wasfor the purpose of describing, but not limiting, the invention. Variousmodifications and enhancements will become apparent to those of ordinaryskill in the art and are within the scope of the invention, which isdefined by the appended claims.

The invention claimed is:
 1. A track for traction of a vehicle, thetrack being mountable around a plurality of wheels for driving andguiding the track around the wheels, the track being elastomeric to flexas the track moves around the wheels, the track comprising: an innersurface for facing the wheels; a ground-engaging outer surface forengaging the ground; and a plurality of drive/guide lugs projecting fromthe inner surface, each drive/guide lug comprising: a plurality ofelastomeric layers that includes a plurality of elastomeric materialsdifferent from one another; and a non-elastomeric layer entirelycontained within the drive/guide lug, spaced from a periphery of thedrive/guide lug, and disposed over and astride a given one of theelastomeric layers that is beneath the non-elastomeric layer.
 2. Thetrack of claim 1, wherein the non-elastomeric layer is a polymericlayer.
 3. The track of claim 1, wherein a modulus of elasticity of anon-elastomeric material of the non-elastomeric layer is greater than amodulus of elasticity of a given one of the elastomeric materials. 4.The track of claim 1, wherein the non-elastomeric layer reduces apotential for crack propagation in the drive/guide lug.
 5. The track ofclaim 1, wherein the elastomeric materials comprise at least threeelastomeric materials different from one another.
 6. The track of claim1, wherein a modulus of elasticity of a first one of the elastomericmaterials is different from a modulus of elasticity of a second one ofthe elastomeric materials.
 7. The track of claim 6, wherein: the secondone of the elastomeric materials is disposed inwardly relative to thefirst one of the elastomeric materials; and the modulus of elasticity ofthe second one of the elastomeric materials is greater than the modulusof elasticity of the first one of the elastomeric materials.
 8. Thetrack of claim 1, wherein the non-elastomeric layer is thinner than thegiven one of the elastomeric layers.
 9. The track of claim 1, whereinthe non-elastomeric layer includes a first non-elastomeric material andthe drive/guide lug comprises a second non-elastomeric material.
 10. Atrack system comprising the track of claim 1 and the plurality of wheelsfor driving and guiding the track.
 11. The track of claim 1, wherein thenon-elastomeric layer is generally U-shaped in a cross-section of thedrive/guide lug taken in a longitudinal direction of the track.
 12. Thetrack of claim 1, wherein the non-elastomeric layer is shapedsubstantially as a scaled-down version of a periphery of the drive/guidelug.
 13. The track of claim 1, wherein the non-elastomeric layercomprises a top portion and a plurality of side portions that extendfrom the top portion and terminate adjacent to a base of the drive/guidelug.
 14. The track of claim 13, wherein the top portion of thenon-elastomeric layer extends substantially parallel to a top surface ofthe drive/guide lug.
 15. The track of claim 14, wherein the sideportions of the non-elastomeric layer respectively extend substantiallyparallel to side surfaces of the drive/guide lug.
 16. The track of claim1, wherein the non-elastomeric layer is a first non-elastomeric layerand the drive/guide lug comprises a second non-elastomeric layerentirely contained within the drive/guide lug.
 17. A track for tractionof a vehicle, the track being mountable around a plurality of wheels fordriving and guiding the track around the wheels, the track beingelastomeric to flex as the track moves around the wheels, the trackcomprising: an inner surface for facing the wheels; a ground-engagingouter surface for engaging the ground; and a plurality of drive/guidelugs projecting from the inner surface, each drive/guide lug comprising:a plurality of elastomeric layers that includes a plurality ofelastomeric materials different from one another; and a non-elastomericlayer entirely contained within the drive/guide lug, spaced from aperiphery of the drive/guide lug, and comprising a top portion and aplurality of side portions that extend from the top portion, terminateadjacent to a base of the drive/guide lug and contain therebetween agiven one of the elastomeric layers that is beneath the non-elastomericlayer.
 18. The track of claim 17, wherein the non-elastomeric layer is apolymeric layer.
 19. The track of claim 17, wherein a modulus ofelasticity of a non-elastomeric material of the non-elastomeric layer isgreater than a modulus of elasticity of a given one of the elastomericmaterials.
 20. The track of claim 17, wherein the non-elastomeric layerreduces a potential for crack propagation in the drive/guide lug. 21.The track of claim 17, wherein a modulus of elasticity of a first one ofthe elastomeric materials is different from a modulus of elasticity of asecond one of the elastomeric materials.
 22. The track of claim 21,wherein: the second one of the elastomeric materials is disposedinwardly relative to the first one of the elastomeric materials; and themodulus of elasticity of the second one of the elastomeric materials isgreater than the modulus of elasticity of the first one of theelastomeric materials.
 23. The track of claim 17, wherein theelastomeric materials comprise at least three elastomeric materialsdifferent from one another.
 24. The track of claim 17, wherein thenon-elastomeric layer is thinner than the given one of the elastomericlayers.
 25. The track of claim 17, wherein the non-elastomeric layercomprises a first non-elastomeric material and the drive/guide lugcomprises a second non-elastomeric material.
 26. A track systemcomprising the track of claim 17 and the plurality of wheels for drivingand guiding the track.
 27. The track of claim 17, wherein thenon-elastomeric layer is shaped substantially as a scaled-down versionof a periphery of the drive/guide lug.
 28. The track of claim 27,wherein the top portion of the non-elastomeric layer extendssubstantially parallel to a top surface of the drive/guide lug.
 29. Thetrack of claim 28, wherein the side portions of the non-elastomericlayer respectively extend substantially parallel to side surfaces of thedrive/guide lug.
 30. A track for traction of a vehicle, the track beingmountable around a plurality of wheels for driving and guiding the trackaround the wheels, the track being elastomeric to flex as the trackmoves around the wheels, the track comprising: an inner surface forfacing the wheels; a ground-engaging outer surface for engaging theground; and a plurality of drive/guide lugs projecting from the innersurface, each drive/guide lug comprising: a plurality of elastomericlayers that includes a plurality of elastomeric materials different fromone another; and a non-elastomeric layer entirely contained within thedrive/guide lug, spaced from a periphery of the drive/guide lug, andshaped substantially as a scaled-down version of the periphery of thedrive/guide lug.
 31. A track for traction of a vehicle, the track beingmountable around a plurality of wheels for driving and guiding the trackaround the wheels, the track being elastomeric to flex as the trackmoves around the wheels, the track comprising: an inner surface forfacing the wheels; a ground-engaging outer surface for engaging theground; and a plurality of drive/guide lugs projecting from the innersurface, each drive/guide lug comprising: an elastomeric layer; and aplurality of non-elastomeric layers, wherein an outermostnon-elastomeric layer of the drive/guide lug that is closest to aperiphery of the drive/guide lug terminates within the drive/guide lugin a cross-section of the drive/guide lug taken in a longitudinaldirection of the track.